Dry mouth from meth is probably making the roof of your mouth sore and possibly blistered.
I'm amazed you can even eat tbh. When I'm on meth I literally flee the room if I see or smell food in what I'd describe as borderline-psychosis revulsion. I've walked past a restaurant before on meth and spontaneously puked. But I'm one of those people that goes from like 120lb to 80lb in a few months on amphetamines because I walk around the streets like 18hrs a day and never eat.
How is your oral hygiene?
I have bulimia for 11 years and I can't drink anything even slightly chilled without a straw and anything with spice or salt (even just like potato chips) BURN the fuck out of my tongue and upper mouth.
Related: New Years Resolution #1: Get a new dentist (maybe porcelain veneers, but not sure if I need them).