A long time ago I had a girl friend with the same thing. It seemed to appear when she smoked which she did only occasionaly or when stressed like at church in particular. Her doctor said it was e coli. and prescibed Antibiotics ! Which she was already taking for another problem. I think the Antibiotic may have been the cause in the first place. maybe a good probiotic or maybe coloidal silver may help or maybe even a parasite cleanse. Good luck