bad breath sinus infection

Bad breath??
My 3 year old has been on medication (amoxicillin) for a sinus infection, which often seems to have one year. After the last dose, he has been having a really pungent smell coming from his mouth. I'm not sure if it is because of the medication or if your breathing. This is the first time that his breath always smelled of cake. I brush my teeth day and night and I just dont know what do.And is also the same smell eveytime is sooooo strong. Please help!
Make sure you brush your teeth.

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