i have made vast improvements on my squats(from 225*15-315*12)but my lower back cant seem to keep up.i stretch all the time.i use proper form.nothing seems to help.my back just starts to kill me during squats.an hour later the pain is gone.ive tried a belt and it has helped.no lower back pain at all.should i use a belt?i dont want to lose my core strength though.please help!!