Thyroid

Well, I was told I have hypothyroidism, and I am taking medicine, but my eyes are fading sight-wise. I’m 67 female...I know the thyroid gland controls the brain, heart, stomach, and almost everything. I also have heart disease and am pre-diabetic. I have excessive sweating and dizziness sitting, lying, and standing right now, as I have been right for the last 2 days, and it comes and goes. I’ve changed my eating habits too; I am eating healthy, walking 3-4 miles at least 5 days a week. Is all this due to my bad thyroid? That’s my question. I drink a lot of water but it comes out as fast as it goes in... occasionally I get headaches and pain behind my eyes and ears. Had an ear exam with negative results. I don’t feel I’m being diagnosed well, or is if it's true that it’s all due to my thyroid?