I am sorry that you suffered from hives for so long. I can only imagine. I know that hives is common for Hyperthyroidism. I believe that you can have hives for either HYPO or HYPER. You should read The Thyroid Solution by Ridha Arem. It is my bible nowadays. Reminds me that it isn't in my head ONLY! Good luck!
You really need to see a allergist, hives that last more than six weeks are considered chronic and your probably going to need some blood tests done.Here's more info http://www.acaai.org/public/advice/urtic.htm. I'm suffering from chonic hives right now and its due to high thyroid antibodies. My allergist has not prescibed cortisone because it is only a short term solution and the hives usually come back with a vengence. I am presently controlling my Hives with 10 mg of Zyrtec and then 50 mg of Benadryl, both taken at night. Here is a list of potenial hive aggravating foods and medications: beer, berries, chocolate, citrus, nuts, shellfish, tomatoes, wine. Medications: Aspirin, Non-steroidal/ antiinflammatory drugs (such as Alleve, Advil, etc), and codeine preparations. Try to limit the intake of the above foods and medications while your hives are actively flaring. GOOD LUCK!
Have you cortisol levels checked also. I suffer from hives especially in the sun but have normal thyroid levels (so my doctor says) but my cortisol levels are low.