Having a diagnosis of Hashimoto's, one then must begin on a great education. This site is one of many that offer those who share what they have learned about living very successfully with the disease, some even claim that they have "cured" or greatly reduced all symptoms. Until you do learn by trial and error what works for you, It is highly encouraged that you do take the Synthroid (T4) if it works for you, or the many (T3 T4) natural combination medications, like Armour Thyroid, or NatureThroid.
One of the many things that you will learn about is "gut health". In my 30 year battle to regain health and quite a measure of normalcy with Hashimoto's, gut health is always there at the center. Adding natural gut fauna and flora to the digestive tract is one way to nurture the gut. Learn to make your own saurekraut, or kimchi, or any one of a number of other naturally fermented foods and eat at least 1/2 cup of these things daily. Kombucha Tea is another fermented drink that has now become quite available to buy at everyday big grocery stores (that have an "organic" / health food isle). One doctor told me that if you buy saurekraut, do not buy it in plastic or tin, but only in glass (apparently the plastic and tin bring bad things that outweigh the good of good bacteria). Staying away from antibiotics, alcohol, gluten, dairy, and the list goes on is another way to protect "good" gut bacteria that can be destroyed by these things / cause hives. My son gave me a gift of a "canning jar" type fermentation kit that came with a bunch of recipes. Cabbage and salt and time (as in 21 days) are the 3 main ingredients for home-made saurekraut. Functional Dr.s are the best type of Dr. to help you win the battle with Hashimoto's. They treat the person, and yes, use blood tests, etc. but they also listen when the patient says, "I feel worse" or "I feel better". I've come to know that hormones (thyroid, estrogen, progesterone, testosterone, and more) also play a big part in healing. Vitamin D3, selenium, methylated B Vitamins, and Vitamin E are essential in returning to health. Even if you do not suffer from indigestion, consider adding digestive enzymes to a daily vitamin regime. Remember, the disease is centered in the gut. Consider what many call a "10 day jump-start" of fruits and vegetables only (both raw and cooked and fermented) to "re-set" the gut. Not advocating a vegetarian diet, but again, giving the gut a rest while it heals. As you return to eating other foods after the 10 days, you may notice (if you add back different foods gradually) what agrees with your gut, and what does not.
I personally have learned that I have two "weak" MTHFR genes, in a genetic test performed by my Functional Dr. Notice I did not say defective. In this day and age of pesticides, GMO, and other pollutants and foreign agents that enter into our food and water, I have what Dr. Ben Lynch described as "Dirty Genes" (in his book with the same title). I must take special care to eat "clean". (More of the veggies, less of the sausages, cold cuts, processed food and GMO grains). Page 119 of Dr. Ben Lynch book on dirty genes discusses hives in connection with a dirty DAO gene.
All of the above is not easy, and my busy lifestyle of a working mother, grandmother, highly active volunteer, living on the farm, does not lend itself to indulging in hours of pampering of self, nor planning macrobiotic meals. So, I may never be fully healed. I may have to settle for feeling good for a greater percentage of the time. What I do know and have experienced is that it is possible! It has been years since I experienced really bad hives (which are scary), and looking back, it was in conjunction with what was most probably some other disease associated with a tick bite. So, Hashimoto's in combination with any virus / bacteria / fungal type infection stacks up to a body that screams in a "hive" way, "do something".
Why do more women than men suffer from Hashimoto's? Why does the percentage (some estimates are that a much as 40% of women worldwide suffer from some form of autoimmune disease (fibromyalgia, lupus, chronic fatigue) of those who suffer with Hashimoto's increase every year? Why is it that main stream Dr.s do not understand Hashimoto's, nor seem to care about learning? (including endocrinologists!) The answers to these questions and similar are elusive at best, criminal at worst. That is why we must treat and educate ourselves with diet, lifestyle modification, vitamins and herbs.
Read, read, read everything you can get your hands on as to restoring gut health. Find a functional Dr. Share what works for you - please.