Leg/muscle cramps are often caused by other things, such as potassium deficiency, so if you've had a recent Comprehensive Metabolic Profile, check to make sure your potassium levels are within the normal ranges. If you haven't had CMP done, you should ask your doctor for one to make your electrolytes are in balance.
Excerpt from Thyroid Manager - Adult Hypothyroidism...
"Muscle symptoms like myalgia, muscle weakness, stiffness, cramps and easy fatiguability are very prevalent in hypothyroid patients 23,24 . Weakness in one or more muscles groups is present in 38% as evident from manual muscle strength testing 22 .The symptoms are aggravated by exposure to cold. They are also prominent during the rapid onset of hypothyroidism after surgery or 131I therapy. Impairment of mitochondrial oxidative metabolism provides a biochemical substrate for these complaints, as evident from a rise in the ratio of inorganic phosphate to ATP in resting muscle and an important decrease in phosphocreatine in working hypothyroid muscle with a greater fall in intracellular pH than in controls 1,2 . Transition from fast type II to slow type I muscle fibers is involved in the change of muscle bioenergetics 3 , which is probably multifactorial. One patient with disabling muscle cramps was found to have reduced a-glucosidase activity in a muscle biopsy; after therapy with T4, the symptoms disappeared and the muscle enzyme activity returned to normal 4."
The most important thing is to get your biologically active thyroid hormones, Free T3 and Free T4 optimized. If you will please post your thyroid related test results and reference ranges shown on the lab report we can help assess your status.