Muscle weakness seems to be one of the side effects for me and it is affecting everything I do. I also get ather side effects like itchiness, metal taste in my mouth, swollen nose and insiside of mouth, sore throat and coughing, dry skin, shivering even when warm and urge incontinence, possibly linked to muscle weakness.. I am on 75mg and have been for a year, before that I was on 50mg. I have now been told that I should go up to 100mg after my yearly blood test. This has alarmed me, as I fear all the side effects will get worse. I have an appointment with my doctor to talk this through, but think she will say try the higher dose. I am 62, before being diagnosed with underactive thyroid I had no symptoms of it and it was picked up in a routine blood test. Things have gone down hill since starting taking Levothyroxine.