I had a lumbar puncture (almost the same as an epidural) in Nov 09. I felt like I had a deep local bruise in the area for at least a month afterwards, esp when I reached down. I asked my physio and she said the needle goes through areas of muscle etc that don't have such a great blood supply and hence they are slower to heal.
I had an epidural in Jan 09 for the birth of my daughter. I don't remember any bruising after that at all. However I did have the discomfort of a CS which probably masked pain elsewhere.
Please get your pain checked out. The spine is a delicate area and you need to be sure there are no ongoing problems.