Could These Symptoms Caused by Hypothyroidism?

I began taking Lithium a year and a half ago, but only took it for a couple months and have been off of it for over a year. At the same time, I began having difficulty losing weight and began gaining weight despite constant exercise and watching what I ate. I also became constipated for the first time in my life (at the age of 24) and have been ever since. I get ridiculously cold during the daytime. I have aches and pains in my upper back and neck area for no apparent reason, as well as in most of my joints. I have terrific mood swings and feel very tired if I don’t have my daily energy drink (which can’t be helping anything, I’m sure).

Since the symptoms began, I’ve learned that Lithium causes hypothyroidism in 12% of patients who take it. I’ve gained about 15 pounds while at the same time increasing my workouts (I work out 5-6 days a week doing cardio, weight training, and various exercises at my home). Two weeks ago, I had my TSH tested for the first time, and was told that it was “normal” without seeing the number.

If it’s not hypothyroidism, what else could it be? Has anyone experienced similar symptoms? What about fibromyalgia?