4 yr old son had strep throat, scarlet fever two wks ago. seemed almost better after antibiotics. now throwing up and not eating for the last four day?

Strep throat: he need to be seen again, likely strep is back, I see it a lot in practice than few days after antibiotic , strep comes back either from reinfection or incomplete treatment

Viral illness?: Your son has been treated for scarlet fever and he recovered ,now he may be having viral gastroenteritis .He may get dehydrated because of vomiting and not eating.Try to give him cold drink as -ginger ale that is good to decrease vomiting .iF vomiting continues ,take him to E.R.for rehydration .Better get him checked by your doctor .

Recurrence possible: About 5-10% of the time, the antibotic taken does not completely eliminate the strep germ, and when the antibiotic is stopped, it replicates and causes symptoms again. Some children will vomit with strep, but there could be a different cause for the vomiting. Please have him examined at your doctor or urgent care.