Hi, You are having Chronic Urticaria. You are having an attack of Acute Urticaria. There are various causes for this, commonest cause is allergy to some substance that you are using, medicines, foods, etc. It may also be due to infections, etc. But quite often, as in your case, the exact cause cannot be determined. The primary treatment for this is with antiallergic medicines, the antihistamines like Tab. Benadryl. You can also try with another OTC antihistamine, like Tab. Alavert 10 mg once daily. This will very likely control your itching. If this does not help, then you need to consult your family physican or a dermatologist preferably.
You should read up here: http://dermnetnz.org/reactions/urticaria.html http://www.emedicine.com/emerg/topic628.htm I hope this answer was helpful. If you need more information, feel free to ask. For accepting this answer, please click on the green 'accept' button below. Feedback/Bonus will be warmly appreciated.