Sharp sudden pain lwr r abodmen + lwr back. Fever, nause, vominting, oxycodone not working w/ pain, can't walk+sleep, lost appetite. What can this be? Help?

Ovarian cyst, GI eme. Given your age, and the location of the pain, a gynecological cause (such as ovarian cyst or torsion) is a possibility, though you could also have a GI emergency. I would recommend seeing an md in an urgent care clinic for exam and possible imaging if this problem has not resolved by now.
Abdominal pain. Abdominal pain in lower right abdomen which persists needs to be evaluated by a physician. Even more concerning is that it worsens with walking, no appetite and not helped by oxycodone. You must go to the ER right away.
Possibilities. There are several things that this could be, many of which are surgical. You need to go to the ER and be evaluated sooner rather than later. .