What Causes Weakness, Loss Of Appetite And Fatigue For A 54-year-old Male?

I am a 54 year old male who has no energy, stamina or tolerance to heat. This was not an issue until the last 5 years where I would become extremely tired. Since trying to address this issue I have been diagnosed and successfully treated for sleep apnea. I have also quit smoking and am trying to stay active except that I will literally ache with very little exercise. At 5 11 I am currently 260 lbs, down from 277. I am still working on the weight loss as my target is 235. Sexually inactive as well. Trying to make positive lifestyle changes since I started feeling progressively worse over the last 5 years. I am concerned that although I have not stayed as active as I once was, with sports, hiking, biking that something else might be going on. Every once in while, I feel normal and can do anything I want only to suddenly the following day feel simply awesome. Any idea s are much appreciated.