How do stds work?

I just went to the bathroom and odd enough I felt something weird at my hole. It didn't feel like a bunch of bumps but it wasn't smooth either. I don't know if it was tissue or what but it had a weird texture. But it wasn't just one it was like a certain spot in there with this weird feeling. If you have an std that causes bumps will it's only occur inside or outside ass well or both or what? I've been tested for everything possible except ones that require an outbreak to test the fluid. It didn't hurt or sensitive but it was weird. I've only had one partner he says he's clean but honestly I'm freaked out