Help I hurt my back today at work what should I do?

I didn't start to feel it until I sat down then when I stood up I had a sharp pain in my low back. It's a deep sharp pain. There is nothing that stood out in my mind today that I see as a direct cause but I am doing a housekeeping job right now so I am bent over a lot scrubbing things then when I stand up straight my lower back is stiff. This movement is unavoidable at my job so I tend to ignore it which is a little easier when I'm warmed up and moving around but not so much now that I'm at home trying to get comfortable. I have been doing moderately physical labor for about 5 years and I want to take care of my back because I like being active and physically fit and healthy. I'm graduating college soon so hopefully I can get a job that doesn't involve too much more lifting or wear on my back.

In the meantime should I report this to work? What stretches can I do? What should I avoid? I also have a problem sitting for too long then standing up. Is this just something better posture could fix?