Have you checked into the symptoms of hypothyroidism? Such as dry/brittle nails, thin hair, dry skin, lethargic (always tired, depressed, find it hard to get out of bed in the morning)
If you are having these symptoms, it's possible to be in the "normal" range but still have levels that are too low for you. Every one is different.
Not to say that you are, but I've noticed a lot of posts on here from people wanting to blame their weight on an under-active thyroid. There is SO much more to hypothyroidism than being overweight, and In general, ONLY 5-10 pounds of body weight may be attributable to the thyroid,
depending on the severity of the hypothyroidism.
http://www.thyroid.org/patients/broc...and_Weight.pdf