How can I decrease Lumbar and Hip pain?

I'm a 40 year old male who has had back problems for about 12 years now. I have a very physical job lifting approx 45,000lb/day, 25 -50lb at a time, 10-12hrs a day. I originally injured my lower back and was sent to re-hab for about 6 months and overcame most of the problems. Then re-injured it twice more over the years after starting this job, (same type of re-hab), one was as serious as the first and the last time wasn't as bad.

I still feel pain in back on the right side between the hip bone "bump" and the gluteus, especially when bending over. As of the last time I injured my back, the x-ray showed some flattening of the lowest disk. I was told that this could be normal or related to the problem. A guess would say it was about 30% flatter than the other disk in the ex-ray.

I stretch hamstrings, at least 3 sets of 5, 1 minute to a side, a day, morning, lunch, evening, and then some extras thrown in there when I feel them getting tight. I also do trunk rotations, (lay down, bend knees, throw them to one side and arms the other way, hold one arm at elbow for a better stretch, 2 sets of 5 , 1 minute or longer each). Also, a back stretch,(lay down, pull legs to chest and hold 1 minute, 2 sets of 5). I do the low back trunk stability exercise 2 sets of 10 ,(the one where you get on hands and knees and lift one leg and the opposite arm hold for 5 secs). After doing a set each of the above, I sometimes still have 6 inches to go when I bend over and try to touch the floor, (I'm 6'2" by the way).

I just took a week off work, and by the end of this period I was feeling only about 10% of the pain that I feel when I was working. Obviously, if I got a different job the problem would probably go away completely over a short period of time, but I like what I do and the pay is great compared to most jobs in this area. Still, I think about getting a new job , selling the house so I can afford to live, etc.

The one thing I have learned after all these years is that my hamstrings seem to be the cause of the pain I feel in my lower back on a daily basis. If I keep working and don't do a couple hamstring stretches every hour, (that adds 40 or more minutes to my already long day), I get what I call a micro injury, makes that spot in my hip/back hurt worse.

I think that I already do enough stretches on the hamstrings, to the point they get sore quite often, so I don't know how to improve them any more than they already are..

Maybe they are getting overly exhausted and if I could build some muscle there it would help?

Is there any hope of making my hamstrings longer yet?

Any help on this problem would be greatly appreciated.
Thanks in advance,
Mike