Lower back issues

[Susan]

I have been having issues with my lower back for years. First, it was only noticable when I had "overdone" it - heavy garden work, extra long hikes or something like that. Over time it became a chronic issue. My back bothers me, no matter if I am standing, sitting or even lying in bed. It's in the lumbar region and doesn't go down into my legs. I have a very stiff back (the lower part won't bend at all) and very tight hamstrings (can't reach my toes bending down).

Knowing that back pain is mostly cured by training the muscles around the problem area, I tried to work on it by myself, but mostly because I didn't know what exacly I should do without making it worse, I asked my doctor about it and she prescribed 14 PT sessions and massage.

I really hoped that this would at least result in some pain management, but 2 month after starting the PT sessions I have to say, I don't notice any change to the better. If anything it got a little worse. Because it was so bad for some days in the beginning (which was, according to the PT, normal) that I could hardly move, I tried some exercies from a book called "Foundation training", that DH brought home. It has some routines for strengthening the back muscles. If I do the routines, I really notice some pain relief.

Here is what bothers me: the exercises in the Foundation book seem to contradict the exercises I got from the PT.
My PT told me to "tuck my tail" (sorry but I just can't figure out what tilting the pelvis "backwards" or "forwards" means - I always confuse them) for most exercises - there where some for the lower abs, some lying on my stomach, some sitting on a Pezzi ball and stretching exercises while standing. To come back from a bend down position for example, she told me to bend my knees, tuck my tail, and come up in a "rolling" movement.
This movement with tilted pelvis hurts my back, but I though maybe this was necessary to get improvements.
The Foundation book basically tells me to do the opposite - extending my back and bending my knees when I bend down. Very similar to what you do when you do squats in weight lifting (if you don't know what I mean, there are some videos on their website: http://foundationtraining.com/video/...n_how_to_move/). Coming back up from a bend over position you try to keep your back extended.

Since the Foundation exercises feel good and seem to help, I went on doing them, but still, I'm confused about the two different approches. From my understanding, I must do something wrong in my everyday movement patterns, else my back wouldn't hurt so much (so I'm not convinced that I know what is best for me, I can't go just by feel). But am I supposed to "tuck my tail" to protect my back, or do the opposite? The natural curve of the spine goes inward in the lumbar region, doesn't tucking your tail bend this part in the wrong direction (or is this wrong direction on purpose, some kind of stretching move?).
If I have to lift heavy things (like garden soil or kids )- what is the right movement pattern? Can I safely assume that I do it the same way as squatting, with extended back?

I'm only 33 (and on some days my back makes me feel a hundred years old), and really fear to not be able to move at all some day, if I don't get this sorted out.