Am I Pregnant?

So, on August 31st, I had unprotected sex with my boyfriend. We did two rounds. The first time, he used a condom, but the second time, while we were doing it, I told him to take the condom off. He did pull out in time, and this wasn't the first time we used the pull out method. That day, my period had ended, which wasn't unusual

The next day, I felt like I was starting my period, but I wasn't. I've been having back pain, and a lot of gas. I was having nausea, a while back, but I think it was from me freaking out, and making myself sick over it. But I am still having back pains. No headaches, spotting, or sore breats or throwing up. My stomach is pretty sore though, when pressed on. My period is expected in 12 days.

my boyfriend says we have nothing to worry about, because I freakout all the time about this stuff..

I know sperm can be in the precum, but it's rare, and happens if they don't pee afterwards. But could there have been residue left from the first round, though we waited an hour in between rounds?