Could I be pregnant?

So lately I've been thinking I'm pregnant every time I have sex and assuming that's what I'm doing this time. Before this I trusted the pull out method and never became pregnant. But recently I started birth control (I'm on my 3rd week of taking it). A couple days ago I had sex with my SO two days in a row, twice every time, and he came in me both times. I keep reading about birth control failing but I think it's unlikely. My period is in 9 days and I've been cramping/constipated the last 3 days with no end in sight. Am I just overthinking it for the 4th month in a row or... (Please don't lecture me, I'm aware birth control does fail but it doesn't seem likely)