My back has been hurting recently expecially when I sit down I get a sharp pain sent up my spine and it gives me nausea what could this be?

Disc degeneration. It could be degeneration of a disc between the bones in the spine. The downward pressure on the spine is greater when you sit than when you stand. You are young. If this pain is not intolerable concentrate on strengthening your abdominal muscles. This may go away. Keep your back straight and lift things with your legs. If things get worse instead of better see a doctor.
Unknown. There are multiple causes for lbp. If the pain persists or becomes worse, see your doctor for further evaluation.