I'm currently 28 weeks pregnant and really suffering with leg cramps in the middle of the night. It's been every night for a week and they wake me up because I go to stretch in my sleep and the cramp takes over. It's unbearable and lasts about 4/5 minutes and leaves me with painful calves for days after. It's getting really tiring now as they wake me up so often and interrupt my sleep. Any tips on how to prevent them?