Itchyanyitis

I have had an itchy anus for the past 14 (!) years. I have tried switching soap, shampoo, laundry detergent, diet, I didn't even get relief while on a 14 day master cleanse. I've been to all types of doctors, and tests. It's not pinworms, and I've had stool tests negative for parasites, but am beginning to think it is some type of parasite. I just can't imagine what else it would be. No creams, anti-biotic or otherwise have ever helped. When it's very bad, it's like a big welt around my anus. I cleanse with mineral oil after bowel movements because a dermatologist said it was from fecal soilage, but I don't think so. The first dr. I went to just said it was something I'd have to live with because she couldn't figure out what it was! Anyone have this? Anyone get rid of this? Anyone know what it is? I've done a 10 day Para-free drops and also 4000mg of co-q-10. I'm starting a Bowel Cleanse tomorrow with Bentonite and psyllium (but not sure how long I should do this for). Any suggestions or knowledge would be greatly appreciated!