i've recently realized that people have been teaching us to lift weights the wrong way. weak backs are a problem for 95% of the people in the gym, and i've found that its a humbling process to fix the weak back. we spend all sorts of time doing leg extensions, smith machine squats, and machine rows, and the result is a very strong upper back and legs and a horribly weak lower back. then we try to do a real squat or try to pick up a stalled four stroke and the lower back screams in agony. if we spent our time doing compound exercises like bent over rows, deadlifts, and military presses from the start, our lower backs would develope along with the rest of our bodies. i went through the process of using less weight on the important exercises in order to let my lower back catch up, and it is wortwhile but not fun.
also, i would stay away from weight belts becuase they are a crutch that will allow you to work with more weight than your back can handle, and they will only prevent you from developing the lower back strength that you need to develope.
try to reduce the weight that you use and choose your exercises wisely. your lower back will quickly develope if you train it.