I have been going through a very similar experience- thinking my way through a complex causal chain of muscular imbalance whilst putting up the constant upsetting discomfort of having your body not work properly. I have got to the stage where I think the root cause can be traced back to either dysfunctional ab/core muscles or gait/foot problem( I have both and at this point am not sure which causes which or whether they are co-founders of my physical dilemma). The tight, painful back, tight hip flexors, weak glutes etc for me were just part of the chain.
So yes, I second looking at your core muscles but also suggest you focus some attention on your feet and gait and see if there is any issue there.