You are suffering from what Dermatologist call urticaria. Common causes are food allergy, infection or drugs taken for some condition. It presents with itching resulting in formation of red rashes which we call hives or wheals. Although in most cases cause remains unknown in spite of a thorough search. It can be symptomatically treated with antihistamines so that you do not get any new hives. The treatment should be prolonged until it resolves which usually takes 1 to 6 months. Please contact me through online consult option for further details and treatment. Better antihistamins are available than the ones which you have used. In some cases like you, urticaria can persist for years.