What Causes Cracking Noise On Back After Heavy Lifting?

LIfted a heavy jar of change from the floor, felt a quick pop on my left back lower side. To the left of the spine, I felt what I thought was a pulled muscle pain for first 3 days, but now the pain is in my left groin/hip area and the top of my left thigh has a small numb area. I cant stand straight or walk to long with the pain being horrible. I have a very high tolerance for pain. Ice/Heat/robaxin/ibufprofen/rest after 8 days has not really helped the groin pain. Sittinf isnt so bad.