TSH may take months before it becomes normal during treatment of hyperthyroidism but you need to continue medications at least for a 12-18 months. I would suggest you reduce the dose to 10 mg twice daily. You can have T4 and TSH done every 6-8 weeks. Thyroid related eye disease can have variable course, in fact sometimes it occurs after treatment but in most cases there is a relief after medical therapy, which you are taking. Low TSH does not cause weight gain. You must be gaining weight now because you are getting normal. During state of hyperthyroidism one loses weight.