Cramps In Abdomen, Neck, And Foot. Difficult To Breathe Or Move. Taken Magnesium. Help

Hi,
I have been suffering with paralyzing cramping in my abdomen, neck and sometimes my foot. The cramping is so excruciating that I have to pull over if I'm driving and lay back to stretch it out (in hopes the stretching will help), it could last anywhere from 10 mins up to 30 mins or longer; The BEST I can describe the pain would be like a charley horse but in my stomach or neck, you can actually see my stomach pull in toward my back. When it happens, it's difficult to breathe or move. My doctor thought it might be weak muscles from have 5 children, but when she found out I have to pull over when driving, she said that wasn't normal. She did prescribe to me magnesium, but it doesn't help. There is no reason why or how it happens, it just happens whenever, If I yawn, my neck will lock up, if I reach for something, somewhere on my stomach will lock up(right side, left side, groin area, under my ribs (left, right or center), I don't know how else I can describe it. I'm hoping someone will know or has heard of this before.