What Causes Cramps In Calf Muscle And Toes?

I take 50 mg Losartan (for high BP) and 500 mg Niaspan ER at night for plaque build up in carotid. Problem I'm having is severe calf and toe cramps that wake me up. Is it from either of these? Dr. told me not to take any potassium w/these. Also have side affects from the Niaspan (burning and stinging for 30 min. or so) but have been told it disapates after about a year.