Welcome to the board. What type of doctor have you consulted with so far? The epidural injections are a common place to begin treatment. Often it is enough to allow the patient to begin to heal on his/her own...but two is a fairly good indication that you won't get any results from a third injection.
Are you an athlete? Spondylolysis shows up in young people, particularly those who engage in sports or activities --often playing football for boys/men.
I had sponylolisthesis, which is similar, involving a slipping of one vertebra over the top of the other. In spondylolysis, there is usually an instability at the segment where it occurs, which is often at L5-S1. This can result in chronic back pain. and can cause mechanical and compressive back pain symptoms, which you are experiencing with the nurabness in your foot. The nerves at the segment that is involved can become pinched as they leave the spine. This can result in pain down the leg and into the foot, nurabness and sometimes there is a weakness when attempting to raise the foot...(if compression is at L5-S1).
Conservative treatments are tried first, such as you are using. Patients' activities are limited or restricted. Physical therapy is recommended in an attempt to build up the muscles surrounding the spine, in an attempt to overcome the unstable segment. Sometimes doctors recommend a brace that prevents movement that will make the condition worse. When all else fails, and it is determined that the pain is coming from an instability, surgery may be recommended. In this case a fusion is the surgery that is used to stabilize the segment.
If you are not seeing a spinal specialist, I would highly recommend it. You are in a good city in which to find highly qualified orthopedic spine surgeons and neurosurgeons who specialize in issues of the neck and back....Good luck and let us know how you are progressing.
