I think you better take him to the vet?? Unless it's just a bad tummy ache or something, but for a dog to cry out it sounds like it could possibly be a little more serious than that!! Good luck and let me know what happened when you find out!!!!
If he is continuing to do this, I would take him to the Vet.
I wouldn't wait until he does it again, make an appointment, take him in and have him tested for pancreatitis.
Pancreatitis can be fatal if it isn't addressed correctly, and what you describe him doing is typical of dogs that have the disease.
If he does have it, he will need to be hospitalized for at least a week at the onset because he will be put on IV fluids and THAT'S ALL for the first week. No food or water is given, the ONLY thing he gets is intravenous fluids because the pancreas must have COMPLETE rest for the first week so that it can begin to heal.
After he comes home he must be on a very low-fat diet, since foods that are high in fat can be a cause of pancreatitis. Dogs that eat a lot of human food are more susceptible than dogs who eat strictly dog food. Fatty human food will not CAUSE pancreatitis in a healthy pancreas, but so many breeds today are overbred (and pit bulls are one of the most overbred breeds out there next to labs) that they have problems that nobody even realizes they have until something like this happens. If the pancreas has a problem, the fatty human foods will exacerbate it and cause pancreatitis.
Please let us know what the vet says. Please don't wait. Take him as soon as you can.