Few things, first the bar appears to be in a high bar position? This is difficult to determine with the camera angle. Ensure your feet are shoulder width apart and pointed approximately 30-degrees out. Also, setting your knees during the descent and shoving them out helps you maintain the back angle. This should help with the lumbar flexion. Your eye gaze appears to be looking straight ahead, this will kill hip drive.
Personally, I would lower the weight, buy a belt, shoes and work on proper form. Watch this:
https://m.youtube.com/watch?v=QhVC_AnZYYM