MiraLax Salty Mouth, Allergy Tests, Nite Guard, Mouth Cause, Oral Products

I really don't know if Miralax is causing this side effect but I have been on Miralax for 3 years and then starting having problems with sores, burning and salty mouth. I had the sore removed by an oral surgeon and it came back as chronic inflammatory mouth , cause could be food, meds or oral products like toothpaste, mouthwash and etc. I did have a new night guard made and noticed after three nights my mouth started burning and I got a sore and had allergy tests,egd, went to ent Dr. and had X Rays and went to an internet, dentist and oral surgeon. I also have eliminated foods, drugs and don't wear a night guard and even went off Miralax and a stool softener with no improvement. I went back on Miralax and still even if I'm on it or off it I still have a sore mouth. what am I to do????????