I've wondered if mine has to do with thyroid also. I was tested many times over the years, and was always just on the low side. Once was actually in the low and was treated for a month or so. I just started taking Kelp capsules with the hope of them giving my thyroid a little boost! Glad to hear you have found your problem and are able to keep it in check.
Isn't it a beautiful day in the Pac NW today? Spring is MY time of year!!!!! Moderate temps, and the bursting colors just make my heart sing!
Have a wonderful day!