Mason, get a video of your squat to get it checked off as being OK. 100x4 after only squatting once before sounds like you may not be doing it correctly.
Okay, I did do a lot at lower weights and I've watched a hell of a lot of youtube videos on form as well as getting an experienced friend to help me. I know this doesn't mean my form is correct so I'm happy to do what you asked. As a side note I've always had really strong legs, I have been going to the gym a lot it's only I've started squatting recently.
Also I'm about 90% sure my form isn't perfect anyway as after I did the heavier weights, my lower back wasn't in pain so to speak. More it was tense like as if I had done quite a lot of back exercise which leads me to think I'm using too much back not enough legs. However, I had been deadlifting close to 1RM the day before so it could have been DOMS. Regardless, next time I squat, probably 4-5 days from now, I'll try and get a vid for you guys. I look forward to your advice .
EDIT: Just remembered, I think I was 'folding' too much, ie not keeping my back upright enough. But it's hard to tell when you're on your own.