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The soreness and the bleeding from the lips is due to the mucosal inflammation following administration of the antibiotics. This does not happen with everyone who is having tonsillitis
. It could be reaction to some medicines. You need to consult your doctor (preferably a specialist) at the earliest for a thorough evaluation and change of the antibiotics.
Also, give your child plenty of warm water to drink, glycerine can be applied over the lips to prevent dryness and the inflammation.
Dr. Naveen Kumar N.
ENT and Head & Neck Surgeon