Very bad back pain, both lower and upper back

Patient: I have really bad back pain, my posture is really bad, my back hunches and i’m only 20. the muscles on my upper back heat up and i think its because of my posture, also im a hair dresser so always on my feet etc. my lower back arches in, my hips sway forward, i need to train myself to stand properly but its really hard because my back just goes that way, when i bend down my lower back shakes like vibrates and if you put your hand on it you can feel it. and i can feel it through my body.. if i lay on my stomach and then after a while i get up, my lower back is very sore and i stretch it and it cracks really badly. I also cant use certain machines at the gym like the leg press because my lower back is in agony afterwards, it hurts to take a deep breath because it like clenches up… what do I do? and why is it like this? ive tried to see a gp when i was younger when i first noticed pain and all he told me to do was bend down and cause it didnt hurt me he said im fine and that was it….

Symptoms: Aching back, poor posture, muscles heating up.