See an endocrinologist, get all the tests done ( blood tests, thyroid scitigraphy, etc ). You would have accelerated pulse rate, higher than normal blood pressure, unusual weight loss, trembling hands ( when held out straight in front of you ) and even protruding eyes ( Grave's disease associated with hyperthyroidism ).
The endocrinologist will give various option, ranging from drug therapy using carbimazole or radio iodine therapy or surgical removal of the thyroid gland.
All options should not affect your medical license as long as your condition is controlled. However, if the carbimazole therapy is employed the AME will have to be satisfied that your condition is stable after a 2 or 3 weeks period of monitoring; you may be put on beta blockers or other hypertension drugs to stabilize your blood pressure.
If the radio iodine therapy or surgical option is employed, and your thyroid gland is rendered inactive, then you will have to be on thyroid hormones for life. No problems in maintaining your license but again your condition must be stable. However countries with tough medical requirements like Korea, Taiwan, Japan and China may give you trouble if they do include thyroid function in their blood tests.
Good luck and happy landings!