It appears that u had accidentally bitten ur cheek and that has resulted in an injury. This will subside gradually within a few days. For pain relief u may use a mouth ulcer gel

Hi, looks like you have developed oral ulcers...Avoid spicy and sour foods until the ulcers heal.Drink plenty of fluids.Regularly rinse your mouth out with warm, slightly salted water.Keep your mouth clean.Take pain-killing medication, such as paracetamol.Apply antiseptic gel to the ulcers.Use a medicated mouthwash.Use steroid gels or tablets.Treat aphthous ulcers with anti-inflammatory drugs. Consult Physician...