Deadlifts are a tricky one and as Phil mentioned, the pain it is most likely a result of poor form. I know for myself it did take me a while to sort out my form and still to this day I need to really think about my setup and execution of the lift.
There are a lot of books out there that cover proper form but the one that helped me the most was CT’s Blackbook. In there he has a section devoted to olympic lifts and a step by step overview of proper lifting form. That, and the book itself is really resourceful and draws on a lot of sources like Supertraining for inspiration.
Another thing worth looking at are ways in which you can decompress your spine after lifting. Because with most movements we are consistently putting pressure on our lower back and core, it is good practice to relieve that pressure from time to time.
I typically do three things for this. One, lying on my back and holding my knees to my chest for extended periods. Two, hang from a chin up bar and let my legs go heavy. And three, hold myself up on a dip station letting my legs go heavy.
Aside from that you can lie on the floor with your feet elevated to relieve that pressure.
Hope that helps.