I got them really bad when I was PG with my DS, the Dr said it was lack of calcium so I took an extra calcium tablet as well as my normal pregnancy vitamins, also the Dr told me to stretch out my calves before I went to bed each night and I found that worked wonders, each night that I forgot to strech were the nights that I woke up in agony with the cramps. I remember if the calf cramps for too long it will feel like you've pulled a muscle. *touch wood* it hasn't happened so far in this pregnancy.

Good luck, I hope it gets better