my doctor told me extra calcium helps avoiding muscle spasms
Yeah, water and potassium should help some. Try a glass of water and a banana for a bedtime snack. When they hit grab your feet and pull them up toward you to stretch the calves out. I get woke up in the middle of the night screaming with them. They're very common, I get them when I'm not pregnant as well if I've had a long day on my feet and didn't drink enough.
It may be varicose veins, they are horrible!!! try elevating your leg, drinking lots of water, not standing for long times, otherwise just make sure you're hydrated and you can try stretching out your legs a few times a day, also try eating a banana and upping your potassium intake.