Yes, orthostatic hypotension is treatable, if that is what you have, you could also be anemic. I'd go back to the doctor (or find another) and explain about the new symptoms. (worsening fatigue, pains, weight loss)
Treatment for hypo depends on what type it is, I have neurally mediated hypotension and I'm careful not to stand too long, not to jump up out of bed and to get enough salt in my diet. Your symptoms sound like anemia to me but I'm no doctor.
You'll have to get a blood test to find out.
Here's two info pages, one on the different types of hypotension and another on iron deficency anemia:
I hope you feel better!