I have been on levothyroxine for about 6 months. The last 3 weeks I have had aching in my legs - it feels how it would feel if I had run a marathon the previous day. Extra painful at night, but that maybe because I'm focusing on it more then. Legs feel so heavy and wobbly. I'm normally fairly fit and not overweight, haven't been doing anything unusual. They seem to work OK though. Any ideas?