there is an autoimmune condition called pemphigus that causes blisters, but they tend to be large. My mother is going through something like that and they are ending up biopsying and culturing them. She thought it was shingles but it did not respond properly and behave properly, then they thought the usual yeast/infection kind of thing. Now they are looking at some autoimmune conditions like Behcets and Reiters, but there are so many of these kinds of things. So far, steroids helped. It can be from the sun as mentioned above, or even something that started as one thing, like herpes or staph (oh, make sure you get to the health dept or somewhere to make sure its not a staph infection, that is key and some docs aren't so good at catching that, but family practice usually is or the other places). It scars bad and is very contagious. The other thing can be one type of infection that then has a secondary infection, from havnig it so long.
I just think sometimes the docs are overly optimistic about how quick we should heal from these sores. It takes us a long time to fight any sort of infection so a three day window for herpes might not be appropriate for someone like my mom, who is on a tremendous amount of steroids and is older and herimmune system just is breaking down.
I hope you get it cleared up. Staph can be blisters like that. If you really have trouble, a dermatologist might be the best way to get it resolved, they are my heros lately because they really test and seem to resolve things like this and don't mind sick patients, at least mine doesn't.
Take care and if you get them in your mouth be sure to at least call in and get some special mouthwash or something from your rheumie, because they can last a long time if you don't do anything.
Ills--Sjogrens-Lupus cond., AI polygland. dysfunction 2, hyper/hypopigment, scoliosis,kyphosis,stenosis, deg.,O.A.,spine surgeries, salivary/lymphectomies, NASH, COPD, RLS, UT/GI bleeds, hystero, brain/nerve damage,TB
Meds--INH,Plaquenil, Evoxac, Metformin, Synthroid, HCTZ, HRT and Lidocaine patchs, Voltaren gel, Klonopin, Vicodin, Restasis, Albuterol, steroids