What Causes Chronic Muscle Cramps In Thighs?

I have been suffering from violent muscle cramps since 2007. The first episode was both thigh muscles at the same time. I was rolling on the floor and screaming. I was taken to the hospital and the doctors did not have a clue as to the cause. I was shocked. Subsequent to this, I spoke with a nurse about my experience and she told me that it sounded like an electrolyte imbalance. I did a little research to identify electrolytes and began to carry potassium with me. I never know when it is going to happen. Usually, the potassium will end the cramp in about 3 minutes. Prior to potassium, I would suffer 10 minutes or more which seemed like an eternity! I had one today which was different. The potassium did not work. I am crying and screaming. I cannot talk. I took 2 magnesium tablets in addition to the potassium and it finally let go. I want to know WHY!!!! I have recently learned about drinking too much water and I have lowered my daily water intake to reserve my sodium. I have told many doctors about my suffering but I mostly get ignored. Or, they will do a blood test and tell me everything is fine. No, it s not fine or this would be happening. Any ideas?