Please help I'm only 18

I'm gonna give the whole story so y'all have all the information. I'm 18 and have been on birth control for a little over 3 years. Last Wednesday and Thursday my boyfriend and I had unprotected sex both days but I am on birth control as I said. I have never missed a birth control pill the whole time I've been on it (knock on wood) and this month I have only taken it like three hours later than usual but that was at the beginning of the month. These days that we had unprotected sex (the only days we had sex this month) were a week before my period. On the first day (Wednesday) he didn't cum and on the second day (Thursday) he pulled out and came. On Saturday I noticed dark circles around my nipples. Like the outermost part of my nipples is darker than the inner part. This made me very nervous because I looked it up and everything said it could be a symptom of pregnancy. I know that birth control is not 100% effective but even if my birth control failed we did not have sex during the ovulating week. So now it's three days before my period and I think I'm having mild cramps but I don't know if they're period cramps or pregnancy cramps. I'm really scared and need some really good responses. I'm not really sure what to do and I don't know if I could easily be pregnant or if I'm just paranoid and nervous! Please help!