Weak Lower Back Arch

I injured my lower back a couple of years ago and i havent been able to get this straight. Whenever i bend over a little i lose my lower back arch and it turns into a hunch. I have been stretching my hamstrings but it hasnt really helped.

Which other muscles contribute to a limited pelvic posterior tilt? To be able to even come close to touching my toes i need to hunch my upper back like crazy