I think I have an infection in kidneys. Now it hurts in my back. I have an artificial shoulder. Should I seek help?

YES..ASAP!!!!! You need to see a doctor and get on antibiotics immediately! if your prosthetic joint becomes infected, that is a major problem. You could be left with a non-functional joint or even an amputation. Infection is also bad for your kidneys. A kidney infection could lead to sepsis, which is infection in the blood, and death. This is not something to take lightly. Please seek treatment now!
Pain. If you have an infection of the kidney, it can cause back pain. This should not effect your shoulder, however if left untreated could result in bacteria in your blood stream. A simple urine test can help determine if it is an infection and if so, oral antibiotics should be able to help.