Lower back and back thigh pain while i bend backward.

I can give you a few thoughts. I guess it's only sciatica that goes down the back of the leg BUT:
1) Are you standing when bending backwards? If so, are you tightening your buttocks muscle? Maybe tightening this muscle is causing the pain down the back of your leg.
or
2) Thee is the "foraminal opening" (Do a Google search) where the nerves exit the spinal canal. It opens up when you bend forwards and gets smaller when you bend backwards. This is okay if you are healthy. But if you have what is called "Stenosis" (which happens more in older people over 50-60-70) a nerve could be getting pinched.

So your problem could be either muscles OR nerve IMHO.

Do a Google search for:
"femoral nerve tension test"
This will explain it for you.

I would suggest stretching your hip flexors if it does not make your symptoms worse.
1) Lunge stretch (Do a Google search)
- This works better if your front leg is up on a stair or chair.
2) Your piriformis muscle is tight:
- "[PDF] Seated Hip Stretch" (Do a Google search for the one by "motionwise"