After reading the other womens responses, the heat!! and heat stroke makes you sick (vomit) too, my son got heat stroke from the 4th of July and was rather exhausted and his ezcema flared up so bad the worse ever from the past 1 1/2 years. So the heat can mess up a little one, and not even be in the sun. My 4mos got heat rash the same day too.
But back to the vomit, my dd has been spitting up the past 2 days which is soooooo unlike her. She screams for a few mins I try to settle her and puke. and not just once several times in a row before she stops then the next feeding same thing, ugh! I'm only giving her 5-6 oz which is less then usually 7-8 oz I'm hopping a bug is just trying to get through her system. And no fever either.
I would just call an advice nurse too, they are usually very helpful.
I would really worry if his temperment changes, like he is listless or unresponsive, or just not himself.
Good luck hope he is better soon!