With my son (my daughter I was on bedrest for the last 4 months) I had WICKED bad cramps not only in my calves, but more so in my shins....almost like shin splints....it was terrible!!! I would just usually rub it out, or something. I never asked my DR about it, I figured it was normal. But good luck to you, kick those feet up and enjoy your pregnancy!!
During my pregancy with my son I had the worst cramps in my calves, usually at night. I think it started in my second trimester if I remember correctly. It would keep me up at night. I also got them during the day a couple of times. I was told to eat foods rich in potassium to help eleviate the pain but it didn't help me much. Two of my cousins and my mother told me they experienced the same thing.
I would try eating raisins, potatoes, bananas or kiwi and see if that helps.
Good Luck!