Welcome and thanks for your question,do not worry,at your age,the possibility of this being cancer is extremely extremely low.
In most cases,cancer produces additional symptoms like breathing difficulty, hoarseness,trouble swallowing or on the other side the tonsils swelling last longer than 6 weeks .
So right now ,like your doctor said this is probably a viral infection and nothing else. If the swelling does not go away,consult your doctor again,he will prescribe you antibiotics.
If the swelling continues after taking antibiotics ,your doctor will perform additional image tests and a biopsy if it is necessary. But I am sure this is not your case,so you do no need to worry about this .What you can do is taking plenty of fluids ,drink hot soups adding a pinch of black pepper or make a tea with water,honey,ginger and lemon . Drink that tea 2-3 times per day , you will feel better and it will speed up the the healing process.
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