I second and third the magnesium advice - worked wonders for me throughout my pregnancy! One of the girls in my preg swimming class said she was told to take it in the morning, not the evening, as it can be a stimulant, but not sure how much truth there is in that theory?! I just took it in the morning with everything else I was taking so I remembered.

I only had 2 actual cramps that got me out of bed, but there were some days it just felt like they were just 'under the surface' and ready to go, iykwim? I tried to stay more active on it and ready to jump up and walk if I thought it was going to take hold!