For nighttime leg cramps, I vouch for taking two potassium gluconate (99 mg elemental potassium) tablets before bedtime. I take them each night, and my bloodwork shows that my potassium level is right at mid-range. A friend who is a doctor recommended magnesium citrate and that might work for you too. Do not take magnesium with vitamin D3, it inactivates the D3.
Another thing to know is that some statins will cause nighttime cramping. The first statin I took, which I cannot remember name-wise, caused really severe cramps in the middle of the night, normally in the hamstrings.
I now take rosuvastatin (Crestor) that does NOT have the cramping side effect for me, but there are several statins that will cause severe cramping.