Could be alot of things although in my opinion it sounds like hives or (urticaria).
You could try using an antihistimine such as clarityn (you can buy this stuff at your local chemist) and take it for a few days to see if your symptons go away, if they do you can pretty much safely say that it is an allergy related condition and you could then look to see what might be causing it eg(change in detergant, after eating a certain food etc.)
if they dont go away then you should go to your gp or maybe go straight to a dermatologist.
Hope this helps you
best of luck