Small blister like itchy bumps that recur regularly

[Charms05]

I have small blister like bumps that return regularly on the same spot at the base of my left hand middle finger. They are hard to the touch and very itchy. It gets so bad that at a certain point I make sure to break each blister which relieves some of the itchiness. Once a scab has formed the itching usually stops and the spot clears up only to return later. I have been to see the doctor and have been to the chemist, the medicine given only relieves the itchiness slightly but never cures the problem as it returns about every month to two months.