are you keeping your back straght and not letting it bend? try doing the bar and ask somebody to see if you got the form down. try posting up a video of you and we'll tell you if your doing anything wrong.
i dont have any way to post a video ,but my dad watched me do squats ,and he told me it looks like a have a little hump in back. its hard for me to keep my back straight ,so i think i have something wrong with my back
Yes go lighter and get the form down. Honestly if you get that "hump" on your back thats gonna hurt you in the long run same with doing DL gotta keep it straght at all times, never letting your back roll. A belt might help? not really sure i don't use theme myself personally. The only thing i can say it just go lighter and pratice on the form. Good luck bro