Why Is Oxycodone Prescribed In Place Of Oxycontin While Suffering From Fibromyalgia?

I have MS, fibromyalgia and degenerative disc disease. my doctor had me on OxyContin 60 mg a day, twice a day, morning and night. It worked wonders. he also put me on, 120mg Cymbalta which helped with the neurological pain and 15mg Dexedrine ER a day for energy due to a genetic disorder called Beta thalassemia minor, which makes my hemoglobin run from 8 to 10 on any given day. I actually felt normal for in my life. As child I was diagnosed with low so I had to get painful iron weekly. I was terribly sick until I was finally given the right diagnosis. I could keep up with the best of them. (Well, the middle of them) Recently, my doctor has taken off OxyContin and put me on 40mg a day of oxycodone. He no longer gives me Dexedrine so my energy is down again. I have asked for blood to help, and smaller dosage of Dexedrine and he says he won’t prescribe that anymore. I asked him why he cut the Dexedrine and lowered me to oxycodone and his answer was vague and a little strange. I have been seeing him for several years and I have always passed any drug given. Please help me understand what is going on in the medical field or advice my to seek another doctor thank you for help. Sincerely, Edyee