I would get evaluated for cortisol - but with weight loss, instead of gain, it could perhaps be Addison's disease instead of Cushing's. They are the opposite but share a lot of the same symptoms.
Make sure your draws are at the appropriate time of day to be diagnostic (cortisol peaks and then drops during the day in normal people - this is called a diurnal rhythm) and the ACTH is kept cold and spun immediately, and frozen promptly as it degrades at room temperature rapidly.
How do I know this? It took me 12 years to get diagnosed with cyclical pituitary cushing's disease (and I had a prolactinoma too) and I now have addison's disease as I had my adrenal's removed to cure it.
Good luck.