I'm really sorry to learn about your problem.
Mouth ulcers are very common among females. There are a number of reasons but let's discuss what can hep you. You should get your vitamin B12, and blood sugar
levels checked. Vegetarians usually lack sufficient vitamin B12. High sugar
levels manifest as poor or slowly healing wounds/ulcers. You should monitor and modify your diet
accordingly and may require taking vitamin B12.
I would advise you to take cold and soft stuff in your diet for some time. You can use any mouth ulcer
gel for relief. If your doctor has prescribed any steroids, use it in tapering dose and avoid relying on it. You can apply honey on the ulcers. Keep it for a minute or two and spit it out. You can do this 3-4 times a day.