tiny lumps / blisters on back of hands

for the last 12 months or so ive been getting "attacks" of these tiny lumps under the skin that develop into tiny blisters.  Usually they stay for a week or so then they are gone.  The are present on the backs of my hands  - not on the fingers and not past the wrist.  more prominent on my right hand.

Ive got them at the moment but this time they have been there for a couple of weeks.  the lumps came, then the blisters.  the blisters have now gon but the lumps are still present.  They DO NOT itch, burn or present any discomfort.

Last night i noticed one or two randomly on my forearms.

Initially I thought allergy so have changed soap, washing powder etc etc with no success.

I tried an anti hystamine cream - no improvement.

tried Hydrocortizone cream which seemed to make the blisters come out more

got an appointment with my Doctor next week but was wondering if anyone had any clues

thanks