hi..
this does not look like an
allergic reaction since ur son is runnin wit fever...
i hope he is getting his immunity shots as per universal immunisation schedules since ur child is 10 months old he is due for his MMR shot(
measles ,
mumps,
rubella)...get ur child investigated for measles and rubella by serology...and get a chest X ray done...usually it is a viral infection..which will subside on its own ...jus maintain hydration of ur child wit plenty of fluids...and continue to feed him a good nutritious diet(mothers milk plus supplements).
hope ur child gets well soon