Could i be preg?

Leah
Two months ago my bf and I messed around and I'm worried I may be preg. I really haven't had a lot of symptoms just gassy and occasional mild breast pain and my lower abdomen seems to be getting larger. I'm on birth control but the week we messed around was the week I was taking the estrogen only pills. I took a test at 6 weeks and I was neg could I be preg?