I have sever hives which continued over 3 weeks so far. what might be the cause(s)? would telfast or aerius antihistamine meds. work? which one better

Hives.: Books are written discussing the many causes of hives. The most common cause would be a reaction to a new medication or food. It is often very hard to find the precise cause without doing an elimination diet and or stopping the inciting medication. Hives can also be caused by viruses, airborne allergies, cold, heat, friction and internal disease.

Both: For hives sometimes you need to take more than one antihistamine and also higher doses. With hives the cause is found only about 10% of the time.