You have a condition called urticaria
In this condition you get raised red itchy lesions all over the body which come and go.
Inspite of medications it can be recurrent.
There are innumerable causes and its not always possible to pinpoint a cause.
It can be due to food, medication, dust,pollen, animal dander etc.
Its best to treat it at the earliest as it can sometimes cause lip or eye swelling and also swelling inside the throat etc to cause breathing or swallowing difficulties
The treatment would be tab. Allegra
180 mg once in the morning and tab. Loratidine
10 mg once at night. This should be Taken for atleast 2 weeks. After which it can be slowly tapered off.