tender pain or sharp pain?

Are you able to bend forwards/backwards/sideways without pain? Lie flat on the floor and try to lift one leg, keeping it straight. Do the same with the other and then try both legs. If you feel any pain or a tingling sensation in your back or down your legs, stop immediately and if that's the case, you'd best get to a chiropractor as soon as you can.

I can't say anything definitely as I'm not qualified, I'm merely trying to troubleshoot your problem judging from my own experience. But what you can do for now is try not to bend over to pick anything up and be conscious of the way you're sitting as well as the length of time you're sitting for, ie don't sit for too long. Then get checked up at a chiropractic centre as soon as you can.

Form is good.

How tall are you? For those taller guys with long limbs, the knees can go slightly over the toes. No problem with that.

Form looks good. Only thing I can point out is you seem to lose tightness at the bottom, hence there's a little extra movement. For this, I'd say to remember to take a deep breath before each rep and brace your core, which would feel like pushing your stomach against your abs.