this is just my personal opinion, think for yourself and consult a professional before you do anything stupid
I would need more info to make an even remotely adequate guess. If you can be more specific then I can possibly be more specific.
Here are some examples of the kind of questions that get triggered for me when I hear something this vague (I would ask things like this before I would even start a physical):
Were you squatting to depth before 5 months ago? Did anything happen 5 months ago that triggered this (besides switching to low bar)? Why did you decide to switch to low bar? How long have you been squatting? How heavy? So the first month of low bar squatting was fine, but then you started to tighten up, or did that process (of tightening up) start immediately?
Did you always have an “anterior rotated left side”, or is this recent? Are you left or right handed? Did you do some very heavy asymmetrical loading in a stretched position during that time? Are you a woman and did you had a baby recently 
? What have you tried before, to as you say “make your back better”? And what do you even mean by “making your back better”?
You say it starts hurting, were does it hurt? Are you talking sharp pain or numbing, gnawing pain after training, please describe? ETC, ETC
I usually don’t respond to posts like this because most people don’t bother to be specific and descriptive enough and then still want to know what “it” is. To get a better educated guess think about things like this:
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what are your symptoms exactly, what do you feel (pain, tightness, etc.), where do you feel what you feel, when, is it related to specific movements, be as specific as you can.
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how long have you been having these symptoms, any specific moment that started things (physical trauma, etc.) did these symptoms start suddenly or did they appear gradually, has it been getting worse, up and down, steady, etc. Any relation between external factors and (worsening of) symptoms? be as specific as you can.
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Any previous health problems in the area, previous operations, injuries, etc.
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Any general health problems that can interfere with recovery/ healing, (like auto immune disease, diabetes, heavy doses of emotional stress, etc) Are you using any medication that can interfere with recovery or can cause general and/or local health problems, etc. Any drug use?
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Age, sex, training years, example of what you train on average (weights, reps, exercises)
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If necessary post video’s, photos.
Information like this can help making an educated diagnostic guess, especially if cause(s) are unknown and you can’t do a physical. It can also help with ideas for training and rehab.
Going by what you’ve so far described it could be a number of things (but it could also be something completely different)
- possible pelvic torsion or a real SI block (often overdiagnosed, by shitty PT’s, but they can actually happen, where one side is really jammed up)
- shitty mobility in the rest of the movement chain, a tight lower back does not have to be a problem for squats, can actually benefit you and protect your lower back better (it’s supposed to be tight going down the hole). Obviously an exaggerated lordosis is not beneficial.
- heavy lordosis and tightness could be a protective mechanism, so underlying injuries and/or local hypermobility (at disc and facet level) needs to be checked.
Btw, your PT sucked, a little bit of stretching will do jack shit for a serious asymmetry (if that’s even the right “diagnosis”) You would need mobilizations, stretching and some serious (heavy) stability training. IF that’s needed in the first place, because no body is symmetrical.
If the mobility problem lies in another part of the movement chain then it could be enough to get on a lighter weight with a focus on form and mobility. And if you’re not a competitive powerlifter then you could also squat a little above parallel, really, it won’t instantly turn you into a pussy.
Find a better PT, Chiro, rehab doc, etc. or maybe a good weightlifting coach. Have a professional look at it if your left side is really that much tighter to the point where it’s (allegedly) creating these problems. May be important to figure out any possible underlying causes, could even be something neurological.
Anyway this is just my 2 cents (pretty cheap btw), don’t consider this as professional advice, think for yourself and consult a professional (in person) going forward.
