How much weight is usually lost by eating very little in a week?due to diarreah and cramps.stool tests came back fine

See below: The weight that you may have lost is due to dehydration. It will come back as you recover. I don't quite understand your question. If you are worried that you lost weight, make sure you stay well hydrated (gatorade etc, whatever stays down). If you think this is a way to lose weight, it is not.

Depends: No usual amount. Will depend on how dehydrated you became from the diarrhea, what your basal metabolic rate is, and how hard your body is working to fight off an infection.