Not sure what you mean by "too young to have replacement surgery," as hip replacement has nothing to do with age, but what shape the joint is in. Arthritis often is accelerated after a fracture. If you are taking opiates chronically for your pain, I doubt they would be contributing to fatigue and weight loss. There could be an initial period of fatigue, but the body adapts and you don't notice it too much. That is, of course, unless you are keeping yourself pretty blotto with the drugs.
Weight loss and fatigue are vague symptoms that could be from anything, depression to cancer, so I agree, more testing is in order. These sorts of things are seldom sorted out with the first wave of tests, as those only look at the most common causes.
Jan