Sharp lower back pain after standing?

I work as a cashier and get sharp lower back pains towards the end of my shift. These pains are right in the center of my lower back and hurt when I walk or even just standing. The pains feel like someone is stabbing me in the back and the only relief I get is if I sit (it hurts pretty badly when I first sit for a few minutes until the pain goes away) Today, I thought I was going to have to sit down because the pain was so bad, every step I took felt like another stab. (I work self scans a lot and have to walk to help customers) Any suggestions on what this type of pain might be? I know I need a chiropractor or doctor, but I want to see if anyone had had similar issues or could tell me something before I go in.