What is this sore?

Sexual health
1

23, Male, 5'3, 120 pounds, Mixed Race, France, no existing medical issues or medications, non-smoker, no drugs

So about five weeks ago, I engaged in unprotected foreplay with another male. Five days later, I noticed a sore on my anus. It itched a little and felt uncomfortable at first, but now I barely realize it's there. The next day after I noticed it, I got tested at the clinic and all my results came back negative (I'm planning to get tested again at the three month period). I was wondering what this sore looks like? Is it possibly syphilis, herpes, HIV, or a bacterial or fungal infection? Thank you!

These first 3 pics are what it looked like before.

The next 3 pics are what it looks like now.

2

Probably friction. You've got to realize that anal sex isn't natural and really supposed to be. Therefore, the anus doesn't get naturally lubricated. Vagina, on the other hand, is naturally meant for penetration, which is why it has big problem getting well lubricated upon stimulation.

With that said, I strongly believe that what you have was caused by friction. If it still bothers you, you might want to have your doctor take a look at it; he might be able to prescribe a cream that would effectively clear it all up.