Red spots at back of mouth with fever
usually are suggestive of some viral infection.There may always be super added bacterial infection that is why your doctor labelled it as tonsillitis
Worsening of rash may be coincidental or as a result of drugs.The appearance of rash or worsening may occur with some antibiotics in EBV infection
Dull behaviour may be noted in severe infections or after rapid fall of fever. In such situation child should be examined for other signs of severe sepsis
and investigated for same.Ruling out severe sepsis and good supportive therapy must be added to ongoing treatment.