Are you doing high bar or low bar squats? Any equipment, belt, knee sleeves, weightlifting shoes etc?

It's probably a muscle strain or a pinched nerve.

Would be interesting to get some more info about your form. You should aim to keep your lower back in a fixed neutral position if possible. Not just for preventing injures, but also to move the most amount of weight possible.

You can PM me video/clip if you want me to take a look at your form.

I never squatted more than 70kg or benched more than 80 and I got a lot of compliments on my physique. Powerlifters aren't known for looking good, they're aiming for strength, and it also comes with injuries.

If you just want to look good then a classic bodybuilding regiment is for you. Focus more on form, doing your reps very slowly, mind-muscle connection and good diet. Look into Frank Zane - he was never about lifting the heaviest weight.

I think maybe I should switch to a hypertrophy program, because trying to lift for 5 reps in squats sucks balls since I’m lifting my 5RM and having to take like 10 breaths in between reps by the end, or else I’ll fail.

Yep, do that. Still, try to find out the cause by form checking, maybe hire a lifting coach from a weightlifting gym or such.

Also, as for the scoliosis, I don’t have the money to have them crack my back four times a month and take X-rays while nothing changes

Chiropractors are pretty much a scam. Cracking is just treating symptoms, if that. Go to a physical therapist with good credentials relating to back injury/pain.

If you want to stick to squat, try putting feet wider which would probably let you be more upright, if you don't bend at the lower back you might be able to avoid pain.

You can still build nice legs with machines, and lower weight dumbells for RDLs, lunges, split squats, etc. Can do hill sprints and the like as well. For a muscular physique find a powerbuilding routine, that's what worked for me anyway. I stuck to PPL for about a year which got me to a 275 bench & 405 sumo deadlift now, and I've switched to the Arnold split for the past 2 months since my arms were lacking and now they're catching up quickly

I always start with a compound usually in the rep ranges of 5x5, 4x8, 3x10-12 and for intensity I try to aim to possibly fail the last rep of the last set, I usually get a spotter for last set. Afterwards 2-3 accessory movements per muscle that I'm focusing on that day

This only happens when I push myself, but I only make progress if I push myself.

Firstly, remember that there's two modes for muscle strength: mass and endurance. If you ever have trouble with only one (which is usually the mass building) then your body is telling you to focus on the other.

I'm guessing that you're mass building. Consider the opportunity to build endurance and do less weight with a lot more reps/sets. It's your body that should be making the decisions for you, not your brain telling you that you have to progress at some mathematical rate.

You have to ask yourself why you're lifting. Obviously, lifting - in general - is a good thing for your body and health, but what makes a certain routine preferable to another is the goal of your workouts. In other words, why are you lifting the way you're lifting? Are you training for an event wherein the ability to squat 260 gives you an advantage that you wouldn't have if you were only squatting 220? If not, why are you courting injury to get there?

I'm going to assume that your goal is something other than getting the maximum number of plates on the squat rack, so if you're lifting to the point of injury... don't lift as much. Injuries take you backwards, and maintaining is better than that. Either reduce weight, reduce reps, reduce sets, tweak your form, or do a different exercise to work that muscle group.

In short, experiment until you find a routine that gives you what you want without causing injury. Be humble and realistic: we all have physical limits, so don't feel bad about not being able to do what someone else can do, or what you feel you should be able to do, or what you used to be able to do. Some of my 1RMs are comically low, but I don't feel bad or embarrassed about that because I have wonky shoulder joints and I'm older than dirt. I know that the piddly 85 pounds I can bench (before my GHJs pop out) is still 85 pounds more than most people lift, for the simple reason that 80% of people don't lift at all. The only competitor who matters is the guy in the mirror... try to avoid injuring him.

I, too, have one particular exercise where I go balls-out. It's the leg sled. I'm 60 years old and I weigh around 150 pounds, and my lifetime 1RM is 1003.5 pounds (about six years ago). I can't do that now, and I don't think I ever will again, but if I can't do 700+ for at least a few reps I feel bad. The thing is that I don't injure myself doing it. If one particular day I max out at 680 for five reps, so be it: I call myself a pussy and go for more the next time. Fitness isn't a sprint. It's not even a marathon. It's a lifestyle.

Resistance bands solve this. Your body is weakest at one part of the exercise and strongest at another. This is usually the limiting factor for athletes and people lifting but resistance bands can take you further. Lots of sports teams are using them now.