It'd be easier if we could see a video. Biggest thing is form but I need to see. I find it helpful to Squat barefoot or just wear a flat sole shoe. It makes it so much easier to push through your heels. Also you may be using too much weight and I know it sucks but you may have to drop the weight a tad. If you are having trouble falling forward or backwards then you are leaning and not squating straight down and pushing straight up through your heels and too much weight may add to the issue affecting form.