Hi,
There can be multiple causes for rash
1)
Viral rash usually have associated fever ,your son has only tiredness
2)it doesnot appear like
chicken pox because again in this condition you get high grade fever and crops of fluid filled rash.Hope he has received the chicken pox shot if he has then again the possibilty is negligible.
3)eczema or allegic rash coul be a possibility .does he itch?
4)
Fifth disease which he suffered in Jan should not recur because of
antibodies in the body against it.
I think at present apply
calamine lotion .Wait and watch if the rash progresses and if he develops fever get in touch with his docter for evaluation.
Bye
take care.