Suggest Treatment For The Cramps On Broken Ankle

I have a broken ankle that has been pinned back together with a plate and am in a half leg cast. I am getting extreme cramps in the foot under the cast about 2 hours after going to sleep. Nothing seems to relieve the cramps other than getting up and moving around and I am not getting any sleep. I am a 42 year old woman and the break is 4 weeks old I have 2 more weeks in the cast and have been suffering these cramps for the last 2 weeks since I have been in the leg cast