Recurrent Fever

So my son woke up at 4am Monday vomiting every 10-15 minutes and with a fever (101.5). I took him to the ER and they gave him a Tylenol suppository and zofran and an hour later ibuprofen. After about 3-4 hours we were sent home. He continued to run a fever all day Monday and Early Tuesday morning. However Tuesday mid day and afternoon he seemed fine except being tired and not much appetite then his fever spiked again that night. Today he woke up and cried for about 30 minutes straight and acted like his belly hurt and hasn’t had much of an appetite but his temperature was only up to about 99.7. Then all the sudden at 10pm it’s back up to 101.7 but he doesn’t really seem to have any other symptoms other than being kind of tired now and then. He hasn’t vomited any sense Monday morning at the hospital and has played and seemed completely fine at times. Could it be something else besides the stomach virus now? I don’t understand the fever going away then coming back like it does.