Please take the baby to the hospital to see a pediatrician or a specialist for a proper diagnosis, then they would be able to give you the right prescription accordingly to help treat it.

And treated by a doctor.
Also, you may observe the following as FIRST AID measures as you head to the hospital according to Dr Gbemi;
GIVE PARACETAMOL FOR FEVER (high body temperature), apply CALAMINE LOTION to the rashes (TO SOOTHE THE ITCHING).GIVE PLENTY OF FLUIDS'.

Please see your doctor for treatment. Measles should not be treated at home. Measles should be diagnosed