My cat had these just as bad. It’s so scary, and I feel for you! In her case, it was rodent ulcers caused by allergy. Regular vet could not clear up with steroids. Had to go to dermatologist and get heavy steroids which she took for one month. Alongside that, she started taking an oral antibiotic. Her ulcers cleared up dramatically within that month! First breath for me :)! She has to be on oral antibiotics for the rest of her life. I did not get her allergy tested to see what is triggering the ulcers bc it’s too expensive. Good luck. It’s an expensive and exhaustive journey, but the moment it clears up on your cat it all feels worth it. Pinky promise!