Pregnant on birth control?

Hello, so recently I’ve started taking a medication for a Uti. I was on my period and the a couple days after I got up (like two or three days) we had unprotected sex, as normal. I’m still on birth control, but my family said that this medication (bactum) makes it ineffective. But my doctor and everything else says that it probably won’t effect it at all... Also- I’ve been noticing something similar to period cramps but I can’t tell if it’s a side effect or if it’s gas or what. Do you think I could be pregnant?