Many of us hypothyroid sufferers are not, and never have been, overweight. The doctor who diagnosed me via bloodwork looked and me and said, "well, you're certainly not fat! Hmmm..." But indeed my TSH was high and Free T3 and Free T4 were low. I had many symptoms because my body was not, and never will again, produce enough thyroid hormone to keep my body functioning as it should.
Please look at the following thread and read the 12 last posts at the bottom. You will see some of the grave consequences of not taking one's medication:
http://www.medhelp.org/posts/Thyroid-Disorders/What-happens-if-I-quit-taking-levothyroxine/show/478065
As you can see, you can go into a coma and even die if you do not take your medicine. Your body needs thyroid hormone for all bodily processes. Hypothyroidism does not just "go away" on its own. There is no cure. You need to take medication for life. Make no mistake about this. It does not matter if you "look" hypothyroid or not; you are hypothyroid if your hormone levels are low.
With that being said, we don't know your actual hormone levels from just the TSH value. Please post your most recent lab results so we can give you further advice. The tests we are most interested in are Free T3, Free T4, and TSH. In addition, were you tested for Hashimoto's? This is the autoimmune disease that causes hypothyroidism in most people. The tests for that are TPOAb and TgAb.
4-6 weeks after stopping your medication your symptoms will return. Your thyroid will not just "go back to normal". Weight gain was not a symptom for you, but were any of these other symptoms?:
hair loss, swollen neck (swollen thyroid/goiter), edema, heart palpitations, brain fog, depression, mania, sensitivity to heat and cold, chronic fatigue, panic attacks, constipation, heavy periods, migraines, muscle weakness, joint stiffness, slow heart rate, high cholesterol, hypoglycemia, memory loss, vision problems, infertility, swollen tongue (tongue scalloping)