What I hated about losing weight when I was sick (from not eating) is that the muscle goes too, faster, so I still weighed "too much" but my body wasn't use to supporting me anymore and working properly.

Have you had any antibiotics recently? The wrong kind of those can throw things off. I was sick 5 months because one kind of antibiotic was being used but not the other that I really needed. You could have an infection/pain of some sort somewhere hinding under the narcotics. I'd have them do an MRI just for the heck of it :-)