One of my three four month old kittens has taken a bad turn quite suddenly. For the past two days he has been eating less, throwing up white foam and/or yellow-ish bile (multiple times, only ever between 2 AM and 8 AM), had odd gray diarrhea (very wet, but with solid stool, if that makes sense? as if he peed and pooped simultaneously?) and today he's lethargic. He is drinking water, thankfully. He's always been a big eater, and very very energetic. We're taking him to the vet tomorrow but I was hoping someone could give me some advice on how to help him out until then? It's 3 AM here, we leave for the vet at 11 AM and it's a four hour drive to get there, so I'm kind of afraid of him getting a lot worse before we can get to the doc. Thank you for any and all advice.