I used to get cramps during the night really bad too, i still get them now but they are far and few between (watch i'll get them tonight now lol)
I took magnesium tablets and they worked a beaut, it is safe to take them, i enquired on here aswell as asking my GP. Its bubs taking nutrients out of us that makes them worse too, i suggest the tablets and the odd sports drink, the work wonders for me, although i ate bananas at the same time.
Goodluck