The week before last, I had a large boil ... how can I put this delicately?... where no sane lady would like one! I was having trouble walking, so went to my GP's surgery, where a Nurse Practitioner prescribed a week's course of antibiotics (Flucloxacillin). Now I was quite pleased with this, having read from other people here that their CFS/FM symptoms had sometimes improved when they've taken antibiotics for an unrelated problem. Boy was I mistaken. Within 24 hours I had a dozen ulcers in my mouth and on my tongue, I developed another boil the size of a walnut on my behind (couldn't walk OR sit down comfortably - great!) and developed a rash on my hands. 24 hours after I finished the course of antibiotics, both boils went down and the ulcers cleared up and I still have a small patch of the rash on my left hand. None of these are on the list of contraindications that came with the tablets, so - did I just get unlucky and over-react? Has anyone else had these sorts of mild reactions to penicillin-based antibiotics? Would be very interested to find out.