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
)...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