Recurring Severe Burning Pain In Waist Line Area, Worsened With Sleeping. On Loratab And Sulfasalazine For Pain. Cause?

A friend of mine says she has a burning pain on her right side in her waist line area. She says it is so excruciating. She says that if she sits up it is relieved a little but it starts hurting more when she lays down. She ends up having to lay on her left but there is still very heavy pain continuously. what can be the reasoning for it. She says she ends up taking loratab and sulfasalazine for the pain but this symptom keeps returning. What can be causing this burning pain?