STD?? Help!

Okay I'll give a bit of background info:

My boyfriend and I are in a gay relationship and I am a trans male, so I'm biologically female. We've been together for 6 months. Going into the relationship we were both free of STDs. He did get kissed on the lips by some girl at a bar. We've kissed since and I've given him head.

Now, I noticed about a month ago that a bump appeared on my anus. It doesn't hurt or itch, nor is it growing or changing. It's slightly more yellow than the rest of my skin. I have no clue how long it's been there, but I'm not experiencing any symptoms connected to it. Should I be worried?