When I sit and lean. Forward my lower back really hurts, and when I walk allot my foot is getting really numb... What could it be?

Not sure. The info given is limited and not specific to one problem. Possibilities include low back disk problems (like a rupture or herniation), spinal stenosis (narrowing of the nerve channel in the back causing nerve irritation). Foot numbness can also be caused by nerve problems unrelated to the back.
Alot of things. You should see an orthopaedic spine specialist. Be examined...Get x-rays and an MRI to get to the bottom of this.