Be sure to push lots of fluids ... ie. water. Could you be getting a little dehydrated making you feel crappy and no appetite? It doesn't explain the pain, but sometimes scar tissue forming during the healing process can cause discomfort. Try to keep moving a little. Maybe lay down flat and roll from one side to your back to your other side. Sometimes that will help. Trapped gas can cause awful pain -- rolling will help that too.
Do you have a fever? Did you do the "pinch" test to check for dehydration? Any other symptoms? Leg cramps? Do you have lots of gurgling noises from the intestine? Is your abd. distended or swollen?
Try to eliminate all caffeine and sugar... both will cause diarhea. I know this from years of experience. Try the foods that will help to solidify your output: oatmeal, rice, pasta, potatoes. But most importantly, drink fluids: water, gatorade, etc. If you are loosing that much fluid, your electrolytes are probably wacked out. Try to get them replenished.
It wouldn't hurt to touch base with your surgeon/doctor tomorrow morning. Labs can tell if you are dehydrated. Let us know what happens....
Diagnosed with CD in 1979, many resections and meds
Perm Ileostomy July 1984 at Cleveland Clinic
Disease free since surgery