First I'd like to say that I'm sorry to read about your girlfriend.
It sounds like something is going on, but is it a physical something or an emotional something? I would certainly go to my family doctor...maybe print out this post and mention all the different symptoms and weight loss. He/she can do some bloodwork and check you over, then the two of you can go from there.
I wish you so well and hope you let us know how you're doing.
Welcome!
KD