I hope when you say you've been lifting for a while that you mean a few weeks, unless those are by some chance 100lb plates, in which case a couple months would be ok. Otherwise, you should definitely be lifting more weight, and be bigger yourself.
That said, regarding your squats:
- Big breath, hold, and set your back between each rep. Stop breathing in on the way down, and I don't see you setting your back.
- Unlock your hips and knees together. You're currently pushing hips back first.
- Cut off about 4 inches of depth, so you're an inch or two below parallel. The extra depth is loosening you up at the bottom.
A few more things to fix, too, but focus on those and let's see how it looks.