Sick babies

My little guy just turned 3 months and he's caught a viral infection. Every tome we think he's getting better he gets worse. He's barely eating, his poop is all liquid, he's thrown up a couple times, and he's barley peeing. His pediatrician sent us into the ER but they said he wasn't dehydrated enough for an IV. Then he started eating again. We got all excited bc he was asking for his bottles every few hours even if he was only drinking 1-2oz every 3-4hours. But then he went 10hrs without peeing and then as soon as he finally peed he vomited less than an hour later. We are spoon feeding pedalyt now, but if he vomits again it's back to the ER. I hate seeing him like this.