My lower back hurts every time I do squats, even though I'm using light weight. I try to keep my back straight but the pain doesn't go away. Is it a technique problem or do I need to strengthen something first?
A perfectly straight back isn't actually ideal for squats, and that's probably part of your problem. You need some natural forward lean from the hips, not total rigidity. What does matter is keeping your spine neutral - meaning it follows its natural curve without hyperextending or rounding it. If you're forcing absolute verticality, you're putting weird tension on your lower back.
The pain almost always comes from a combo: lack of mobility in your ankles or hips, weak core, or just a position that doesn't work for your body. Try actually dropping the weight (or do bodyweight squats), keep your knees tracking over your feet, and let your chest go a bit forward. Some people find it helpful to do shallower squats while they fix their movement pattern. If your ankles are tight, that forces you to compensate with your lower back too.
If the pain sticks around even after you fix this stuff, there might be something else going on that means you need to skip deep squats for a while and just work on core strengthening. But before you get there, focus on technique without load and how your body actually moves, not how you think it should look.
Most of that pain comes from hip and ankle mobility, not necessarily from how you're positioning your spine. I had that same problem a while back when I was trying to do "perfect" squats with my back vertical, and it turned out I was lacking ankle flexibility, so my body was compensating by arching forward in my lower back. What helped me was dedicating time to working on mobility before squats: hip rotations, calf stretches, that kind of thing. If the pain persists even with light weight after you improve your mobility, then yeah, that might be something worth getting checked out by a professional, but it's almost always that.
When I started training, I had exactly the same problem, and it turned out the issue was that I lacked ankle mobility, so my body was compensating by leaning too far forward and putting all the weight on my lower back instead of distributing it properly. Before adding more weight or trying to "fix" your technique, try doing some ankle and hip flexibility stretches for a couple of weeks, and do lighter squats while focusing on not putting all your weight on your heels. Also check whether you're actually going deep or if you're stopping halfway, because sometimes people get stuck right at the point where there's the most stress. If it keeps hurting after that, then it might be that you need to strengthen your core or consult with someone who can watch you in person, because lower back pain during squats should never be normal.
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