I can't say that I've noticed this, but, anything is possible CALynn. You may want to check with you doctors, and also check on line for possible side effects with Metformin.
In fact, I checked for you, and found on page 2, of this info (at top of page) that muscle pain is possible. Check out this site: Metformin Side Effects
I have noticed muscle weakness and leg tenderness when I'm on Cipro, which is used to treat my constant sinus infections.
Pastor Paul from SoCal