I Am Experiencing Foot And Leg Cramping At Night On

I am experiencing foot and leg cramping at night on a regular basis. Since Jan. 2015, I have become much more active, made significant life style changes in exercise and diet (e.g. I now exercise regularly, primarily riding a stationary bike, moderate weight training) and have lost 90 - 93 lbs. I am now in a healthy BMI range and want to stay there. Two years ago, in June 2014 when I was technically obese, I had emergency surgery to repair a fully ruptured right Achilles Tendon, in the leg which I now am getting these muscle cramps. What could be causing the foot and leg cramps? They start if I start stretching my legs in bed and at times include not just my foot/ankle but my hamstring as well. I have to get out of bed to stretch out the foot cramp and if the hamstring starts, I have to react differently to stretch out the cramp there. I am concerned I am not getting something in my diet that could be causing this issue. It doesn't happen each night but happens frequently the last few months. I make sure I drink 8-8 oz of water per day also.