Is my back pain connected to my other symptoms? What is the cause?

[NoxxCipher]

I'm an 18-year old female who suffers from chronic back pain and have done so for about 6 years or more. It was diagnosed as a side effect of stress by a physiotherapist 3-ish years ago, and at that point in time I was going through a lot so it seemed to fit. However, these problems have persisted (even worsened) despite my stress levels being at virtually zero for most of the time since. I decided to reevaluate things recently, and wondered if any of the following could be connected, as well as give a more specific description of my pain.

The pain is focused in my upper and middle back, but shifts to my lower back when my spine is curved backwards or after a long period of walking. The physiotherapist offered me exercises that give some relief but hasn't fixed the problem. The pain is constant, so I've learned to live with it, but intensity varies, feeling like a dull ache or a bruise that can be unbearable. It seems to be worse in cold wheather. I also can't do sit-ups as they're too painful and it feel as though my back is too weak to support me.
I find it difficult to move if lying on my front or bending over for a long period of time, or just on a particularly bad day- these positions also cause pain to occur in my lower back.
When things get bad, I struggle to bend over and have to have help when sitting up, dressing ect. The general ache is bad enough, but the pain when actively moving on one of the worse days has left me sobbing before - albeit rare that things get so bad.
I use a magnetic vest from time to time that uses elastic and magnets to hold my back straight. It helps a little, but the pain after removing it makes me reluctant, and well as the painful marks it leaves on my shoulders and underarms where the elastic rubs /digs into me. Admittedly, I have poor posture, but sitting up straight for long periods of time is incredibly painful even with the use of a vest, and it usually makes my lower back sore and stiff. I will also mention that when the pain first began, my posture was fine.

I can usually 'hear' tingling in my upper back when I move, like a million tiny shifts at once, but I can't feel it. However, I can feel a 'groaning' in my spine every so often, like it's struggling to stretch itself.

My back cracks whenever I move, often in bouts of about four clicks at the same time. Some of them are tiny, and some are so intense that my body visibly lurches when it happens. It's particularly common if I twist or stretch. I use deliberate cracking as a form of temporary relief, asking those around me to give me tight hugs and other methods. Pressure also helps, but often makes things sore to the touch.

I have an occasional sunburn-like pain where even clothes hurt to wear, nothing in particular seems to trigger it.

That's the gist of my back problems, but here's the other stuff;

I suffer frequent/recurrent Urinary Tract Infections - this has been an issue for virtually my whole life, but I feel they are more common now than they ever were. I also cannot afford to keep treating them, so have to stay in this state for months at a time. When I do get them treated, it usually takes less than a month to become ill again. I'm very clean, wipe after going to the toilet the 'right' way, and take steps to drink plenty of water, so I don't understand the cause.

I have weakness in my knees that's gotten progressively worse. I don't remember a time where my they've bent properly, bending inward instead. I can't squat unless I rest on the balls of my feet, and my knees click often (loudly) when I walk. The clicks aren't painful or relieving, just audiable. I can also deliberately click my knees several times in a row by twisting them inward (far more so on my right leg). I've begun to feel less confident when going down stairs as it feels like my knees shake and struggle to hold me, so I often rush, causing my back to hurt more.

I can click my wrist and elbow easily by twisting them inward, and I can also feel my entire shoulder shift if I try to crack it, I can usually do this 2-4 times in a row, though every now and then I can manage 7-ish times with my shoulder -  the shifting settling to a deep clicking instead.

I struggle to stay awake and I struggle to sleep, favouring short naps to actual rest and living with a constant, unedrlying tiredness. It doesn't matter how many times I sort out my sleeping pattern or how much sleep I've had the night before, I will still begin to doze after a few hours of being awake. Sometimes the pain keeps me up at night, but I have a history of depression, insomnia and other such illnesses that might have a part to play. I've also suffered from binge-eating and anorexia in the past, and though I've been better for about 3/4 years, I wondered if that might've caused some issues.

I'm sorry that there's so much, but I wanted to get eveything covered - thanks for any help or advice you might have!