So, how do you know if you're pregnant without taking tests?

I am on the pill, however, last month I had got a uti and of course had to take pills for that. According to the doc, that pill would mess with my birth control. I ended up taking my last uti pill on the same day I started my new pack. (About 2 weeks ago) after about a week and a half after, my S.O. and I had unprotected sex. So here I am (8days later) kinda panicking that I might be pregnant. However I am not experiencing any of the signs. I do have an upset stomach, I'm kinda moody, and I have a headache. My period should start in a week so could that just be premenstral symptoms?