Hello and thanks for your query. I shall make an effort to provide you with good professional recommendations specific to your questions. Irregularities in menses is very common and can happen in any one, even in person who is having regular menses. Discharge looks brown when it’s discharge tinged with old blood that took longer to come out from your uterus. But as you have mentioned about unprotected sex, it can also be implantation bleeding, which occurs when a fertilized egg attaches itself to the uterine lining. One of the earliest and simplest way to know that you are pregnant or not, is by using, urine pregnancy test. Most experts advise that you should wait at least one day after your missed period before taking a home pregnancy test, though waiting a week is considered best. This can be tough when you are anxious to find out if you re pregnant, but waiting allows for a higher degree of accuracy when taking the test, as hCG levels rise rapidly in pregnant women. It s best to do the home pregnancy test first thing in the morning, when your urine is most concentrated and hCG levels are highest. So I advice you to perform a test a week after missed period and with morning sample of urine. This test kits are nearly 98% accurate, so reliable. With transvaginal ultrasonography, the diagnosis of pregnancy can be made earlier by 4-5 weeks gestation. I would suggest you to use one or the other method of contraception if you are not planning to be pregnant. Yet again, I duly appreciate your query to me, I do hope that have found something useful to help you and I shall be glad to answer any further apprehensions. Sincerely,