Hello & welcome, I am Dr. B, a licensed veterinarian and I would like to help you today. I do apologize that your question was not answered before. Different experts come online at various times; I just came online, read about your situation, and wanted to help.
Again I do apologize that my colleagues could not aid you sooner. If you would still like assistance, can you tell me:
What the stool look like? Loose, hard, small pellets? What color?
Are his gums nice and pink (not white/pale)? Moist or sticky?
I suspect you meant the belly was hard but if you press on it, does he have any tensing, tenderness, discomfort, or pain?
Could he have eaten anything he should not have (ie bones, toys, plants, chemicals, human meds, etc)?