Hey lady's

So tonight I put the 5yr old son to bed at 7pm. He woke up at 09:30pm with pain in his back leg so I've massaged with magnesium spray and put a heat pack on both of them till the pain went away. He went back to bed so I went for a shower after I came out and sat down and next minute his back out cry his eyes out took me 20 minutes to find out what's wrong and yep again leg cramps. I don't know what to do to stop them please help. I'm over seeing my boy in pain and his tied too as he has school tomorrow and I'm getting tied and upset (pregnancy 20 weeks). If anyone knows any good tips please let me know. And sorry but if you have nothing nice to say done say anything. Thank you