Sorry, I've been away for a while and just got back home...... have you heard any more about your lab tests? If they didn't do them all, you might want to look into finding another doctor. I had to do the same thing.
I had some of the otjer symptoms. I printed a checklist and marked them and handed them to the dr. they tested me for a bunch of stuff but when they left a message of my results left the important ones out
I have had hypothyroidism for nearly 5 years. You, first, need to make sure they test you properly; meaning they need to test Free T3 and Free T4, which are the actual thyroid hormones, and not just TSH, which is a pituitary hormone which is supposed to signal the thyroid to produce hormones.
You should also ask to be tested for thyroid antibodies and confirm/rule out an autoimmune thyroid condition.
Other than the weight gain/inability to lose, do you have other symptoms of hypothyroidism? Those could include constipation, fatigue/exhaustion, dry skin, puffy "bags" below the eyes or puffy eyelids, swelling in the feet/hands, muscle/joint aches/pains, high cholesterol, slow heart rate, etc. You might try googling "symptoms of hypothyroidism" and compare your symptoms to the list.