Late period

This is my third month taking birth control, so my body is still trying to get used to it. Ever since I got on it, I’ve been sexually active. We don’t usually wear protection but he never finishes inside. The first two months I got my period but the second one I had some brown discharge a week before my period. However, this month I got the discharge and was hoping my period was going to get here but I’m already on the second week of my pills and no period still. I did have sex 4 days ago (knowing that my period was late) and i did take a plan b. I took pregnancy test and one of the tests didn’t show any lines and another test said not pregnant. Should I be worried if I’m pregnant?