You are doing more than what most people are willing to do. Just continue to be there by her side, continue with the back massages, and so on.
I've been struggling with my condition for the past 4 years...it has gotten so bad and such that I focus on the pain/symptoms so much that I can't 'see' or 'feel' the support/love that my friends/family show me...only when I "look back"--I can see/know that support. So just continue doing what you are doing....your girlfriend's at a spot where all she can see/feel is the pain. Just continue voicing your concern/love for her and let your actions show it. Deep down, she is thankful for your support/love...even though she can't express it or acutely aware of that at this moment.
She needs to get her focus off the pain/symptoms--the focus on the pain/symptoms can actually aggrivate the condition, as it does mind.
It is important that she does go to counseling...they have the training/techniques/etc. to help her deal with the pain/symptoms/etc. It has helped me a lot.
It's great for you to be supportive and loving of her--and helping her deal with her condition...but you can only do so much. It will become a big strain on your relationship (as well as her other relationships--such as with friends or family) if she doesn't go to counseling.
Continue to support/love her all you can...but I would get her to counseling and also go back to the doctor (or find another) and look into other conditions that it may be.
If your girlfriend has a Faith (like Christian, Jewish, Muslim, etc.) she can can get help thru her church/synagogue/temple/etc. too.
You are doing more than the 'usual' and your girlfriend is lucky/blessed to have someone like you in her life.
One thing a counselor will tell her is to look at today as 'today' and not worry about 'tomorrow'--to take it one day at a time. That is helpful for both the person in pain and the person who supports.
Good luck!