Can high dosages for 7 years be harmfull to health.

Hello my name is Kim. I was diagnosed with Hyper Thyroid in April 2000. I chose Radioactive Iodine Treatment. The first attempt in June 2000 was not 100% effective. The second treatment was in September 2000. I was started on Synthroid 100mcg. In July 2001 my prescription was changed to Levoxyl 125mcg. In March 2002 I went to Levoxylthrine 150mcg. I was told by the pharmacy "this is a high dose for a women and you should not take it longer then 5 or 6 years. well it has been 7 years and my right hand gets numb and burns in pain. The cold weather makes me hurt. My skin is really dry and my neck is starting to cave in, looking real skinny. I'm not sure if 150mcg for a women of 160lbs. for this long is harmful to my health.