Well, the fact that you had it for years seems to rule out an STD. I would just get it checked out, theres not much i or anyone else here will be able to tell you.
Do you have any idea as to what condition or disease it may be ?
Hey max,
If it has been there and has not changed at all it is likely something else. I have not heard any other STD that can cause that type of situation where it is present for years. Your best bet is to get it checked out , especially by a dermatologist since they are experts in this kind of field.
In my opinion, i do not think it is an STD but you still should get it looked at for a piece of mind. Good luck =)