I go through the mouth ulcers with every flare, and the increased prednisone then brings on the oral thrush - it's a vicious cycle.
The diflucsan will help the thrush but not the mouth ulcers. There is a product called orabase gel you can find in most drugstores which is just for oral ulcers - it helps some. Also plain liquid mylanta, the anracid stuff, apply with a q-tip to the ulcers and let dry. If you can find it in a health food store, slippery elm lozenges are excellent - let them dissolve in your mouth like a cough drop. Also, oddly enough, marshmallows - again, just let them dissolve in your mouth.
You definitely want to avoid using alcohol-based mouthwash as it will just make the problem worse. There are several good non-alcohol products available, Rembrandt, Tom's of Maine, etc.
If you like yogurt, the active cultures in it will help with thrush. Yogurt smoothies might go down a little easier. I try to avoid anything extremely hot or cold or spicy when my mouth is really raw.
Bland soft foods like mashed potatoes, pudding, jello, etc. are also good. If you can tolerate the taste, Ensure or a protein drink will at least keep your nutrition up. They taste a little better when chilled.
If your mouth sores don't heal up soon, your dentist may be able to recommend something. And if you notice that your throat is sore or it's very to swallow, let your doc know asap. Thrush can go beyond your mouth into your throat (candida esophagitis) and this needs to be treated right away.
Hope things start to improve soon.