My 15 Month Old Has Had Diarrhea For 5days Now

My 15 month old has had diarrhea for 5days now hardly eating and drinking. Last night he was waking up screaming I took him to er and they did nothing other then tell me he had a very low temp they released him an hour later without checking his temp and gave me prescription for a stool sample. today has been a little better till now he is freezing cold, sweating, and waking up every 5-10min screaming. He did however eat a lot for dinner and has drink better today. I checked his blood sugar and it is a 97. He has a sister with diabetes. I am very lost and afraid it is pointless to go to the er again.