It sounds like your body has undergone a pattern of compensatory movements. This most likely explains your inability to feel certain muscle groups working and why your posture is less than symmetrical (although perfect symmetry is a myth). I don't know how the this began. It does appear that it has now dramatically affected your kinetic chain.
The IT band needs to have adhesions resolved. Stretching will not accomplish this. And don't forget to SMR as well as stretch the glute max because about 50 percent of it connects to the IT band. A common mistake many IT band sufferers make is to foam roll that area but never address the glute max.
The lumbar spine is NOT something you should foam roll as you don't excessive movement there (it's actually the thoracic spine where we should have the most mobility). That said, you can perform SMR on the Quadratus Lumborum with a tennis ball, baseball, softball, lacrosse ball (you get the idea). You'll have to experiment and see which size and density works best for you. You can also work the erector spinae AS LONG AS direct pressure is NOT placed on the lumbar spine (this is why a ball and not a foam roller or pvc pipe is recommended).
CAUTION! The quadratus lumborum (QL) inserts L2-L5 AND the 12th rib. So be very careful that you don't stab yourself when performing SMR.
Basic blue print:
Address the overactive side with SMR as well as the help of a skilled therapist. I don't know how deep your pockets are; SMR is a cost-effective solution. However, for your case, regular visits to a skilled therapist strongly appears to be in order.
Whether you choose to go with Rolfing, Art, etc. is something you will have to ascertain yourself. It's not enough to just perform SMR or get some type of deep tissue therapy; you will need to stretch as well. Conversely, it's not enough to just stretch as this does almost nothing for the trigger points (by now they are too dense); this is why doing things like yoga WITHOUT working to break up the trigger points is not something I would advise.
Strengthen the underactive side. If you're truly serious about resolving this, uni-lateral movements will be your new best friend.
If you hold a stretch at a challenging (but not painful) level for 30 seconds or more, you should activate the golgi tendon organs. Through a process called autogenic inhibition, your body will down regulate the muscles and minimize their involvement. Take advantage of this during your workouts.
I recommend SMR pre and post workout. Work in the static stretches to fit with your goals. And definitely SMR and stretch post.
All three aspects must be addressed. And don't neglect lifestyle choices as well.