Sudden sharp lwr r back pain+lwr r abdomen, chills, nausea, vomiting, sometimes fever, can't walk, lost appetite, can't sleep. What can this be? What to do?

Sounds infectious. Your symptoms sound consistent with some type of infection which may involve the urinary tract or may involve other structures in the pelvis. An entity known as pelvic inflammatory disease is also possible. If you are or have been sexually active in the past few days or few weeks then, a full examination of the female organs should be undertaken.