Back ache with fever. Of pain and fever?

Severe back ache and fever for past 10 days. Fever with chills, seen once in 24 hrs, mostly around night or early morning hours. Back pain is too bad, unable to sit or lie down on same side for more than 15-20 mins. Bone and muscle pain, oestroporosis recently diagnosed and medication started for same. However orthopedic says muscle pain might be due to some other reasons. Blood and urine tests were done, all reports normal, malaria medication given for 3 days, no improvement. Consulted 2 orthopedics and 2 general physicians, they are unable to figure out root cause, every doctor giving different possibilities. Is MRI a required next step? How safe or accurate it is? Is there any other way to find the root cause of pain and fever?