What Causes Nausea, Vomiting And Poor Appetite In A Child?

My five year old has been febrile since this am; flushed and slight tremors I ve been altering Tylenol and Motrin; poor appetite and slightly less active but not lethargic ; he presented with nausea but no vomiting until this HS but his vomit was very viscous and bile like but it had no foul odor at all; in fact it almost smelt sweet, I m a nurse and have smelt and seen a lot vomit but this just struck me as odd; could it be a blood sugar issue? I m a little concerned he has no related history. He had red jello earlier and bright blue Gatorade minutes before and vomit was not indicative of this at all. I m not a med surg whiz it just seems fishy to me I can t peg it because he complains of stomach upset frequently like least once a month and usually always vomits as soon as he says this so It was different that he hadn t until this late in the course of syptoms but I knew it was coming because it was middle of the night the Motrin was worn off and I had just checked on him and he was hot again in sleep. Should I been concerned more than usual or let it run its course and force fluids.