HI, thanks for using healthcare magic
It is likely a viral infection of the gastrointestinal tract (stomach and intestines).
Viral infections can be associated with a rash which is called
viral exanthem. The rash would normally resolve along with or soon after the other symptoms improve.
The decreased appetite that you noticed is related to these new symptoms of
vomiting and may continue for a few days.
He may also develop
diarrhea though some persons only have vomiting
If the vomiting is severe or there is associated
abdominal pain or any concerning symptoms then he should be seen by his doctor.
If there are no concerning symptoms then treatment generally consists of making sure that he does not become dehydrated by replacing his fluids and electrolytes.
In children this can be done with
pedialyte , if he does not like pedialyte then another oral hydration packet can be used.
Only small amounts are given evey few minutes eg 1 tsp to 1 tbs every 5 mins. If he takes too much, it may make him vomit.
Probiotics may help as well.
I hope this helps