What Causes Painful Cramps In The Mid Of Night?

Good Evening, Im 22 yrs old and a female college athlete. For the past year I have woken up in the middle of the night to leg cramps. The past week the cramps have been very painful. The knots wont loosen up and make it almost impossible to walk. Also, if I rest my leg up it will "fall alseep" within minutes. I have increased my potassium and water intake. In addition, I take multivitamins. Any advice?