Brief Answer:
Tooth infection, cellulitis, medication.

Detailed Answer:
Thanks for your query. I have gone through your query.
As far as the swollen cheek and redness is concerned I have the following possibilities.
It can be because of a tooth infection that had spread to involve the soft tissues called cellulitis. The other possible cause can be a hair follicle infection that has lead to cellulitis.
Nothing to be panic, consult an oral physician and get it evaluated. Mean while you can take a course of antibiotics like amoxicillin and metronidazole for the infection (if you are not allergic).
If there is a tooth infection, you need to get it treated with either root canal treatment or extraction depending upon the condition of the tooth. Do saline gargling. Upload the images of the cheek for better diagnosis and treatment plan.
I hope I have answered your query. If you have any queries reply me back. Take care.

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