It could be fungal/yeast/bacterial infection or it could be parasitic infection,certain parasites lay their eggs around that area.
Have you tried anti bacterial soap,it usually takes care of any bacterial problem on surface of tissues?
If it were yeast or fungal infection,rub some yogurt with live culture on it and see if it works?
If none of these ideas work,go see a doctor,he may take your stool sample to be tested
I do too. Unfortunately, I have no idea why. Hopefully, someone will come to our aid. ANYBODY!?