What Causes Frequently Occurring Hives?

first of all, a little history, i am 32 years old, when i was 17 i was pregnant, and had a horrible case of hives, and nothing the doctor gave me seemed to help, only for about an hour or so..they went on for 3 months, then stopped on their own..last year in may i had another episode,but only lasted for about a week..now i have had them for almost 6 months with only temporary relief, i have had allergy test and, nothing came up, except for penicylen, i was diagnosed with hypothyroidism 6 years ago, but moved to mexico and the doctors insist it is an allergy, i have done hours and hours of research on hashimotos, and i lean toward thinking that that may be the underlying cause, also, for over 3 years now i have had a small lump behind my right ear, sometimes it swells up really bad, and other times its just a little, but i do not have this behind my right ear...please help me with any suggestions.