Experiencing some symptoms which I fear could mean I'm pregnant, but if might just be my head.

I recently had sex (10 days ago or so). We used a condom, I was on my period, and he didn't cum. I am also on birth control, but at the time I forgot to take the pill the day after and I was also on antibiotics which I hear can make the pill a non-factor. Recently I also started to experience discomfort in my stomach including spasms, pain and some swelling (I think it's just belly fat though) accompanied by some minor nausea. I'm wondering if these symptoms mean I'm pregnant or if it is just in my head, or stress related. Please help!