Stiffness and sharp back pain when i am sitting, when i lean forward or walk the pain is shooting and burning in my lower back. what can cause this?

You need : An evaluation of your back as it sounds like your nerves are irritated. Physical therapy may help slimy with antiinflmatory meds and ice in the acute phase

Back Problem: What you describe is irritation of the nerve roots in your lower back that can be due by a herniated disk or spondylitis changes. Need to be seen by your physician and possibly by a spine specialist.