How do you stop cheek biting during sleep?

Dental block. Your dentist may be able to help you. Similar to folks who grind their teeth at night, a dental block may help alleviate your cheek chewing. Also, sometimes stress level reduction can help decrease nighttime gnawing.
Mouth guard. Otc mouthguard cost $20 will help this issue - orally take vit b2. To heel quicker.

Related Questions

How to stop cheek biting asleep?

CHEEK BITING. The dentist will put a dental guard to keep you from grinding teeth while asleep so you can not bite your cheek.

I have been constantly upset/crying my self to sleep for no reason, lip biting/cheek biting, no motivation, self harmed. HELP

You need medicalhelp. Based on your description, you need emotional support and medical help. Please share your problem with your parents and ask them to find help for you either from a Conseller or a psychologist. It is not uncommon to have such problem during teen years but there is medical help available. But you must seek help right away and not delay it.
Get help now. You seem quite depressed and need to see a mental health professional right away. Please have a parent or a trusted adult come with you for an initial appointment. Write down all meds you take, any alcohol/drug/tobacco/caffeine use, current stresses and about when you started feeling so negative. Your pcp is a good person to ask for a referral. If you feel suicidal, go to the ER. Please get help.