Hi,
Assuming that your periods were regular, and you got your period yesterday (? 02-05-2013), your last LMP should have been around 2nd of April. You had unprotected sex on the 20th day from your last LMP, which is almost a safe period. The cramps and back pain goes in favor of menstruation symptoms. But even then as you had only mild bleeding and that too stopped within one day it is better to do HPT/LAB test after 7 days for pregnancy and decide what to do.
Otherwise for you there will not be any problem. Anyhow Luck will not help you always. Keep it in your mind that "PREVENTION IS BETTER THAN CURE".
Best wishes.

Hi,

Thanks for your query.

With the information the you have provided, there is a high possibility that you could be pregnant(Unprotected intercourse without any emergency contraception )

The symptoms you have described like headaches, back pains, cramp & breast pain are non specific. They are due to the effect of hormone progesterone which get secreted prior to your periods and also in pregnancy.

Its very difficult to tell whether you are pregnant or not , based on your symptoms alone.
The fact that your periods have been lighter also raises the suspicion of a pregnancy.

The next step is to meet your doctor who will check for pregnancy by urine or blood test . She may also request a scan to confirm the diagnosis.

Hope this was useful.

Best wishes.

hi there, your symptoms are more consistent with infection of the genitourinary tract rather than pregnancy. It would be wise to get a urine exam done to rule out infection and also an abdominal ultrasound to rule out any pelvic inflammatory disease. You may get a urine pregnancy test also done after a week to rule out any possiblity of pregnacy. Now get yourself treated for the infection if any. Take care.