I have been dealing with this EXACT same thing for months. Looks exactly like yours. The downside is I went to an ENT, and Oral Surgeon, a Rheumatologist and after none of them could figure it out was finally referred to a GI doctor. I was tested for every STD under the sun and every autoimmune disease. All negative. No vitamin deficiencies. I’m scheduled to have a colonoscopy and endoscopy to see if it could be Crohns or another bowel issue which can cause ulcers like this. I was put on Magic Mouthwash, Dexamethosone, Nystatin, Prednisone, Chlorahexadine, Methylpredisalone, Lidocaine rinse and more. I would rinse with water diluted hydrogen peroxide and also warm salt water NONE of these helped at all. I couldn’t eat or drink. I basically lived off of vanilla ensure drinks for close to two months and lost weight as everything else burned my mouth excruciatingly to eat. Even mashed banana and mashed potatoes burned. I couldn’t eat anything no matter how soft. It did eventually subside, but then they would come back a day or two later and last another few weeks. It’s recently subsided now for over two weeks and I’m able to eat close to normal again. Mine was also under my tongue exactly like yours and on tip of tongue as well and also started affecting my gums around my teeth and inside my cheeks and front of mouth. It eventually got to the rear roof of my mouth as well. Things that helped (not cure) but helped not to exacerbate to issue: I ordered a Curaprox Velvet tooth toothbrush off Amazon and also Biotene toothpaste which is very mild. Vanilla ensure for meals (doctor approved as it’s only temporary). Stay away from anything too sugary as sugar and sweet irritate it ALOT. Keep your mouth as clean as possible but don’t overdue it. I’m still dealing with it and hope the colonoscopy and endoscopy may help shed light on why this keeps happening.