What did the dermatoligist say when you went there? Sounds like maybe sensitive skin?? Try using a deodorant for sensitive skin? Sometimes different perfumes and deodorants, antiperspirants will cause irritation. I recently had a problem with what I will call it a scab on my underarm So i used iodine which I bought at the drugstore. I used it for about a week and it actually cleared up the problem But something looked like maybe a bug or something else seemed to come out of my armpit. I know this sounds crazy but I swear something seemed to be stuck in there. I thought maybe it was just from shaving and was irritated. But it actually looked like it was inflamed and kind of swollen. But now it is totally gone. I would go back to the doctor and get it checked out again. All the best