Lower back pain when squatting. What am I doing wrong?

Hey fellow fitness blenders!

I am working out regularly for the past 10 months. I've done the programs "Low impact R2", "FB Complete" several times and just startet "FB Booty R2" two weeks ago. I don't quite consider myself a beginner anymore, more of an intermediate.

I always focus on good form when working out but there seems to be on thing I cannot get done properly: squats. After doing them with or without weights (and sometimes right when doing them) I always hurt my lower back. It's not a stabbing pain, more like a dull back ache. I just don't know why? I have anterior pelvic tilt, maybe it has to do with this fact? Does anyone have similar experience or any advice on how to prevent this from happening?