I have used a bicarbonate of soda solution as a mouthwash, but helped soreness/ burning mouth for me.
It might be an idea to get this checked out- we had a discussion fairly recently, and member LadyDeda found her sore mouth was caused by Lichen Planus, so it was good that she didn’t dismiss this as just dryness due to SjS.
Here’s the link- it might be worth a read as there were some other suggestions too: