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 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. 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 advice you not to take any medication without consulting doctor, as all medications are external substances and they have their own side effects. 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,