My Boyfriend, 56year Male Has Had A Lower Back Ache

My boyfriend, 56year male has had a lower back ache for 2 weeks now. We want to know what could it be. I know it could be a lot of things. I tell him perhaps its that he needs to drink water and stop drinking soda pop because sometimes our back hurts and we think its our back but its actually our kidneys. What do you think Dr.