Why do I keep getting muscle cramps in legs and stomach?

I could just bend over to pick up something then I would get a painful cramp in my stomach in the spot were it hurts it gets hard I would have to lay down for a couple of minutes before it goes away its been a couple of years this has been happening with my stomach I been to the doctor even had them look inside my stomach but nothing just acid reflux but why painful cramps when I bend downor over? Now recently its been my thighs and calves wakes me up in the middle of the night its getting to the point if im just sitting and move a certain way I get cramps I feel like its to regular the job I have to stand for 8 hours.

You need to take breaks during your job work. Also please consult your doctor.