need to vent

So me and my boyfriend had sex for the first time this weekend, and he said he enjoyed it a lot and I could tell he did, and I did as well but I just felt different afterwards as in like if I was a different person because I had sex. Maybe it's all in my head, but it's just been bugging me because I want to be able to have sex and not feel bad afterwards for it. Any advice? Or did anyone feel the same afterwards?