To All Forum Users:
There was a software glitch and for several days a number of questions were misrouted to a server that did not post them properly. In addition, it appears that the automated limit to number of questions each day did not work properly. The result is a serious backlog. My replies to many questions will be briefer than usual, and I need to be very strict in following the rules about questions that duplicate others, especially for obvious low risk situations. You may use the Contact Us link to raise any concerns. Please note that it is not the moderator's decision whether or not to refund a credit card charge.
Also, I probably will not be able to respond to any follow-up comments or questions.
To your question:
I do not make specific diagnoses on line. From your description, as well as the negative tests, you can be 100% certain the problem is not syphilis, herpes, or any other STD. Beyond that, I cannot say anything. It is almost impossible you are '...suffering from some heretofore asymptomatic and rare condition'. See a health care provider, preferably a dermatologist. In the meantime, stop trying to find answers online; you will never be successful in knowing what you have until you are examined.
Good luck-- HHH, MD