It could just be a simple stomach bug or it could be something a little more like Salmonella. My son had salmonella when he was 2 years old and I ended up waiting before I took him in to the doctor. By the time I took him and the stool cultures came back, he was already better. His symptoms were low-grade fever, cramping, diarrhea, and he did have some blood streaks in his BM's. The thing with stomach bugs is that you don't know what it is unless the stool is cultured. Make sure you keep him from getting dehydrated - that can happen very easily kids and since you said he's now not taking liquids, I would take him to the doctor as soon as possible. Good luck and I hope he feels better soon.