My Son, 14, Has Typical Flu Symptoms; Fever, Chills, Sore

My son, 14, has typical flu symptoms; fever, chills, sore throat . But he also has swollen red gums. So sore he can't eat. And they bleed when he brushes his teeth. 3 days of these symptoms. What could it be?
Thank you in advance for your help. Jennifer
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