Swollen and severly sore cheek, sore throat, white patches in mouth on side of cheek. negative strep culture at er, pain meds not working.

Hard to say: This could be many things. You need to be specific about when it started and what treatment has been given. This could be thrush, aphthous ulcers, lichen planus, leukoplakia, and other things. Oral diagnosis can be difficult, so seeing the oral cavity problem is very important. If you give more information, we can help better. Go to an otolaryngologist for exam, treatment, and possible biopsy.