Brief Answer:
With pleasure, please see below.
Detailed Answer:
Hello again dear,
Thanks for getting back to me, I am happy to know that you wish to understand yourself better so that you can make informed decisions about your sexual life.
The menstrual cycle in most women repeats every 28 days on an average, (it may fluctuate by 2 days +/-). The menstrual cycle is a normal physiological cyclical event that happens in normal women who have attained
menarche (attained
puberty and have started menstruating), most girls attain menarche by the age of 12 to 13 years of age, again it is not a fixed age, it can vary from 9 years to 18 years.
These physiological changes occur as a result of the
hormonal changes that happen in the body, these hormonal changes are controlled by the Hypothalomo-hypophysio-adreno-gonodal axis, meaning, Hypothalamus(a part of the brain), hypophysial (Pitutary gland, again a small part of the brain), adrenal cortex, and ovaries are all involved in making these changes happen. All these glands and brain parts interact closely, one stimulates or inhibits the function of the other in very complex ways, as a result of this interaction, as you reach the age of about 12 or 13 years, the ovaries and the
uterus are stimulated to attain physical maturity and the ovaries start releasing the ovarian follicles(The eggs or the ovum) in a cyclical pattern.
Normally, there are two ovaries on wither side of the uterus, every month either of these releases one egg, and they alternate each month, that is to say, if the right ovary releases the egg this month, the left will release the egg next month.
The periodicity of the release of the egg is controlled by the biological clock and resultant hormonal changes, once you reach the age of menarche, the
estrogen and FSH (Follicular stimulating hormone) stimulate the growth of the follicles (Eggs in the ovaries), and estrogen also prepares the uterus by stimulating the endometrial thickening (The inner lining if the uterus), this process takes about 14 to 15 days, as you near 14th or 15th day, the follicle in one of the ovaries is mature enough to be released, so when it is ready, the hypothalamus releases a hormone, which in turn stimulates the
pituitary gland to secrete FSH and LH(Leutenizing hormone) in much higher quantities, this is called the LH surge, this LH surge happens regularly around the 14th day, and this increased secretion of LH and FSH is associated with you noticing an increase in your body temperature, that is around the 14th day, all women have a higher body temperature than other days. The secretion of estrogen which was increasing everyday till this time will start reducing, and as the LH rises suddenly, one of the most mature follicle in the ovary ruptures thus releasing the egg.
This rupture of the follicle is the reason for the mid cycle pain in some women. One more important thing to remember is, due to these sudden hormonal surges, most women have the highest sexual urge/drive on these days, it makes sense to feel increased urge to have sex on the days when you are about to ovulate, as the sole purpose of ovulation is to make babies. As women are more sexually aware around the days of ovulation, mistakes happen on these days mostly, that is they forget to use precautions. (I personally think women become a little bit careless or they choose not to use any protection because the hormones make them feel that way on these days, because that is the evolutionary response that is programmed into our brains over millions of years).
Normally, women fail to conceive on every single cycle, that is either because they do not have sex, or because they use protection to avoid
pregnancy, so when they do not conceive, the released egg dies off and either gets absorbed and is broken down by the body or it gets pushed out, but in anticipation of a successful fertilization the ovaries start producing
progesterone, this hormone starts preparing your uterus, the estrogen in the first 14 days had already made the inner lining of the uterus thick, now progesterone makes it even thicker and ready for receiving the fertilized egg, if you have sex on these days and if the egg does get fertilized, then the fertilized egg will attach itself to this inner lining and will start becoming an embryo and will produce more hormones like Beta-HCG and progesterone which will keep this inner lining of the uterus intact and functioning so that the baby can start growing well.
Since most of the times women don't have sex on these particular days or they use protection, the egg fails to get fertilized, so it will not get attached to the inner lining of the uterus(This is called
implantation and in some women can cause a slight spotting too).
If the egg does not get fertilized, it is wasted, so there is no production of the necessary hormones to continue maintaining the thickness of the uterine wall, so if the fertilization does not happen by 3 days after ovulation, the egg dies off, and the implantation should happen by 7 or 8 days after the egg is released, since this also does not happen, after the 7th day, the levels of progesterone start reducing and both, estrogen and progesterone fall drastically, they reach lowest levels by about 25th or 26th day (that is about 10 days after ovulation), so since there is no stimulus to keep the inner lining of the uterus functioning, the uterus sheds it off on day 28th, this is what we call periods or
menstruation.
This is a very normal process that happens to all women and it goes on repeating every month until you become pregnant or reach an age at which becoming pregnant is physically not possible (
Menopause).
So, from this you must have made a wise guess as to which are the safe days to have unprotected sex and which are not, I will make it even more clear to you, the sperms can survive for up to 5 days inside the uterus, so, if you had sex on the 10th day of your cycle, those sperms can make you pregnant because the sperm is alive on 15th day and the egg gets released on 14th or 15th day. If you have sex on 17th day after your previous period, then also you can become pregnant as the egg can survive for 3 days.
So basically, the time to avoid sex is the time you feel most horny, since it is practically not possible to not to have sex all the times, you are feeling like having sex the most, it is best to use a condom during these days, that is between day 10 and day 17th of your cycle, you should use a condom if you don't want to become pregnant.
Other days of the cycle you can have sex without using a condom, we call this a protected rhythm method (rhythm from the rhythmic nature of your menstrual periods), this is a quite safe method, but it is not as safe as using a birth control pill (
contraceptive pills), since you are sexually active, I would advise you to use the pills to make sure you do not become pregnant when you don't want it.
I hope this answers your questions adequately, please feel free to get back to me if you have any doubts.
Wishing you happy and safe sex life.
Warm regards.