TMI- not sure what is wrong

Tmi-

Okay so months ago while having sex with my SO, he all the sudden freaked out and asked what was wrong with the back of my thighs and at first I didnt understand until I looked in the mirror.

It doesn't hurt, but it never goes away and not sure what is wrong with the back of my thighs... anyone have any suggestions?

Here's is the TMI picture