I just read this message and my guess is something related to the candida problem as I have this condition too and had hives 2 times during these years. Once it took 3 days to clear, the second lasted only for 24 hours.
The first time I had big, swollen, itchy patches and I was scared to eat anything but grapefruit for 2 days and then it was gone. The day the hives appeared I ate some fast food with ketchup (what was very rare as I don't like fast food, I just didn't have much choice at the airport) and the next day I ate something with ketchup again and it got worst - so I guessed it was the ketchup. Don't ask me why I chose to eat grapefruit - some inner voice told me... :)
The second time was different, it started with a little redness above my belly button and then it was growing, but never became swollen, only red, and it was literally travelling all over my body, never appeared on the same place twice and it was soooooooooo itchy and nothing helped. It was gone in 24 hours and never came back (luckily :) )
For my oppinion this kind of condition is a strong signal from your body that something is not right. Be serious about getting rid of that candida and starting the cleansing programs as recommended. Also find out what is the right diet for your blood type - very important! And one more thing - on the thyroid board I've found a story about someone curing herself with a very strickt diet - the very same one we supposed to eat in case of candida!!!!! So my guess is you want to think it over about that medicine you're taking...
I hope my story helped a little. Best wishes!