Hi I'm 61 I've Been On Opiates For Over 20

Hi I'm 61 I've been on opiates for over 20 years and have never had this problem before. I yawned the other day and noticed pain coming from under my tongue. So I went to the mirror and lifted up my tongue and it hurt to stretch it. I than stretched it thinking it needed it. After a couple days I noticed a rash of canker sores. I'm treating it with warm salt water and OTC Kanka. What could cause my labial frenulum to dry out so bad it cracked when I stretched it?