Child Hospitalized For Vomitting, Dehydration. Having Diapers With Just Mucous, Blood. In Pain. Suggestions?

My son is 2 yrs 11 months. He was hospitalized last week for dehydration and vomiting last week. (he spent one night) He has not been eating or drinking much at all since this. Today he presented a few diapers with stool smears in them. Around noon today he had a diaper with just mucus and blood in it. We took him to see his PCP and he wants us to get a stool sample. However, he isn t outputting enough for us to get one. He since his visit with the PCP has had 2 more diapers with mucus and blood. He is in pain, and we called the doctors line. Our usual PCP is on vacation as of tonight until next week, and the doctor on call is one we don t get along with at all. He is not concerned about this at all. He says to just make an appointment tomorrow to be seen again, assuming it was a fissure (when the PCP verified without scoping that this was not the cause of a fissure). I am not sure what I should do at this point. If we take him into the ER, they will just call the doctor on call and he is not concerned. I am, and I KNOW something is wrong! (my other 3 kids have the runs too) I am stuck as to what I should do about this?!