My whole cheek is covered with mouth ulcers. Is there any pain relief?

Yes. What to do depends on what has caused the ulcers. You may want to ask your doctor about "magic mouthwash" with viscous Lidocaine for topical relief. If the sores are viral, then you may also need an antiviral medication as well.
You should see a Dr. You should see a doctor to get full treatment and find out the cause. Depending on your age, this might be oral cancer. Oral cancer usually presents by 50 years of age, and in the form of non-healing ulcers that can be painful. It is caused most by alcohol and tobacco use, including smoking and chewing/smokeless tobacco. The doctor can give you pain meds. And also find the cause of this.