What are some medications to urticaria(skin rashes all over the body)? does avyl work and when does its effect start to appear?

Avyl unsure: The best treatment for hives (urticaria) is antihistamines. Unsure of "avyl" but most antihistamines work within an hour or two. There are other medications for hives, but most allergist would suggest that steroids like Prednisone be avoided unless hives are very severe.

"Avil": (pheniramine) an old first generation antihistamine, would work, but causes drowsiness, newer non-sedating antihistamines as cetirizine, loratadine or fexofenadine, or the third generation as desloratadine or levocetirizine are non or less sedating, longer lasting and don't lead to tolerance, your best bet still if the condition isn't controlled is to see an allergist or a dermatologist, good luck

Rash or welts?: I don't know if you are referring to rashes (which tend to be raised or scaly lasting > 1day) or hives (which are raised bumps lasting for a few hours at a time). If it is an itchy rash, topical cortisone cream may help. If it is hives, then antihistamines may help. Cortisone takes several hours and antihistamine about an hour to work.