Stomach area feels weird after having sex for the first time

I had sex for the first time about three weeks ago, on April 8, a few days before i was supposed to get my period. We used a condom, although I did feel a little bit drip on my leg. The next day or two, my inner thighs and vaginal area felt a bit sore, which I expect is a completely normal physical reaction and my body adjusting. About three days after losing my virginty, I got my period on April 11, and finished it seven days later on April 18.

Now, three weeks after I first had sex, my stomach area has been feeling funny all day. It doesn't really hurt, it feels more like a soreness, or a feeling of burping or taking a shit. Also, before I had sex I used to have a more liquidy discharge a lot. Now, my discharge is thicker and sometimes whiter or a pale yellowish-white.

Is it possible that I may be pregnant, even though I got my period three days after I first had sex? Or could it be an std, even though he said he doesn't have any. Or is this just a completely normal physical reaction to losing my virginity? Has anyone else felt this way after having sex for the first time? I have never done anything sexual before this at all, no kissing or anything, so could this just my body adjusting to something it's never experienced before? Any advice or opinions would be much appreciated. Thank you!!