Your back sounds pretty bad.
I herniated two (L4, L5) disks doing squats eight years ago, so I can relate to back pain.
The first thing you need to do is stop guessing. Make an appointment with a doctor, preferably an orthopedic doctor/surgeon. The first thing he/she will ask is if you have any pain in your legs or butt. If you do, they'll guess you have a disk injury. Otherwise they'll figure you just need physical therapy to strengthen and stretch your lower back. Without an MRI, though, they'll be guessing too so I highly recommend pushing for an MRI exam.
After you get an idea of what's wrong, then you can figure out how to manage the pain and avoid making it worse. Options include chiropratic care, massage therapy, ibuprofin etc.
You need to know what's happening with your back before you go any further, but if you disregard all that at least forget about stiff legged deads. And b fold is right, strengthen the entire torso and you're going to have to start very, very slowly using light to moderate weight on anything involving your lower lumbar.