Skin Endometriosis

I think I may have skin endometriosis.  I have this nodule-like bump on the inside of my butt cheeks (sorry if TMI) that is kind of like a large un-poppable pimple, but it has been there for at least 6 months.  Before this one was present I had another one in another location for about 6 months too. Its so weird, and not at all painful.  I didn't really think much of it until my cousin told me about these bumps she gets around her ears during her period.  Her GYN said it was probably endometriosis, as crazy as it sounds.

I can't seem to find any information or picture on the web about skin endometriosis, besides the fact that it exists.  I will be seeing my doctor in a couple weeks and I can't wait to ask him about it. 

Does anyone have or know anything about skin endometriosis?