/fit/ I think I am fucking up everything because I can't

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/fit/ I think I am fucking up everything because I can't control my spine.
I started out lifting a month ago. Was a fat nerd my entire life, became a skeleton once, then gained some weight. Now I'm somewhere around 25.5 BMI so I still need to lose some weight since about everything is fat with zero muscles. I have literally never done any strength training in my entire life, the only thing I ever did was swimming and cycling to slim down.

Now I've been doing some lifts following SL and I am starting to feel pain in my lower back for every lift. Thing is, my spine is completely fucked from an entire life of being a shut in PC playing faggot. Having zero muscle mass doesn't help either. So whenever I squat, my back gets rounded, which puts too much pressure on it. Deadlifts don't progress because I never like my form since whenever I go above something like 70kg, everything rounds to hell and back. Barbell rows are the "funniest", I can keep my upper back somewhat straight but my lower back always rounds. Can't do a slight arch for bench press either, I just can't control that fucker. Whenever I try to arch a bit it hurts like shit.

So my question is, what can I do to improve this? I feel like it is going to bite me in the ass sooner or later and I want to avoid injury if possible. I got a foam roller if that thing can help and looked up some yoga/pilates related exercises that should help but so far they don't really. I want to continue lifting but my back fucks me over.