Pain in lower back lasting 4 days?

4 days ago i got this twinge in my lower left back out of nowhere. I had bent over (not far, i didnt even bend past my hip) to fill up a wine bucket with ice (not heavy lol) and when I stood up straight i got a sharp twinge and it still hurts 4 days later. what could this be? Im 20 yr old female if that makes a diference. thank you! :)