I know your pain. I'm not going to tell you not to take the Diflucan, but WHILE you are doing that, make a solution of 5 parts water to 1 part vinegar. Use it every hour, swabbing it on your breasts with a cotton ball, and soak it on right before and after nursing. It will take the pain away within an hour, and if you keep using it for a few weeks, it will end the pain completely.
I went through nine months of pain--the shooting pain that you are experiencing--before I found this suggestion in a La Leche League pamphlet. Any time I felt a twinge of pain, I started using the solution again, and the thrush never returned. Most doctors don't know about the solution, though. My doctors didn't.
Trust me, the pain will go away. But you have to use it all the time. And wash your nursing bras, burp rags, anything that gets the milk on it, with a little vinegar. It's the only thing I found that really works (and it doesn't stain or anything, either).