You are a PA in a GP setting and you are seeing a 6-month-old baby who has presented with the mother. The mother reports that her baby had a fever for 3 days. The mother also informs you that the fever has subsided now however she has noticed a rash. On examination you note the presence of small red spots all over the trunk, arms and legs. You also note some slightly swollen glands in the neck. What is your main differential diagnosis?