Hi, 
It seems that you are having 
urticaria.
There are many causes of urticaria.
Like.. Food, infections,worms,sun rays, pollution, pollens, 
cold,physical,pressure allergic,drugs,psychological,immunogic,Internal diseases and so on...
It may be without cause.. Idiopathic.
For perfect diagnosis, you 
consult dermatologist.
He may come to conclusion after taking history and seeng investigation reports of 
necessary blood tests.
Antihistaminics may be taken for long time..
Elemination of cause if found..
I hope you may be satisfied with my answer.
Regards.
Dr. Ilyas Patel MD