Thumb skin peeling. lots of pain in nail/nail bed. itchy, red, and sensitive skin. happens every few months and on thumb only. some kind of fungus?

Doubt it.: Nail fungus infections are usually constant, not intermittent. I'm guessing the pain & inflammation is mostly around the nail. This is called paronychia; if there is a gap between the nail and surrounding skin, that's what it is, and it's caused by a mixture of bacteria & yeast. A dermatologist can give you a topical antibiotic/antifungal solution, or you may even need an oral medicine.