Having problems doing Squats

[14Red88]

hey guys so Iv been having problems doing back squats. But Iv been going front squats fine. When I put some weight on the back I feel like I'm going to fall forward or my left leg caves in. I use to do them all the time idk what's happened. But my fronts have blown up I'm up to 150kg for 6. Yet struggle with 80kg on backs? Any tips advice cheers brahs

I have trouble doing back squats with just putting my arms and hands on the bar it's like my range of motion isn't there to get my hands on the bar back that far.