Is the best way to sort out lumbar and pelvic imbalances, to do strengthening exercises? As it is a weakness in these muscles that has caused the imbalance?

I saw a physio up near london who specialised in pelvic biomechanics and it was he who got rid of the pain in my left buttock/hip with the muscle energy technique (to release spasm in my piriformis). He also said that I had a forward rotating right ilium and I had a muscle energy technique to perform to rotate it back. 2 other things he gave me to do were a neural stretch and a glut med strengthening exercise.
But this was also when I started getting the knee pain. My problem is that I was getting treated for a pelvic imbalance yet my knee pain got no better.

I guess I have no option but to try this treatment again.
Its just that any glut med strengthening exercises then aggravate my knee even more. Could this be that I am tiring my glut med so my biomechanics are even worse and therefore my knee gets sore quicker?

I am going to try very gradual increases with my clamshell exercises to see if I can build up strength without hurting my knee. Does this sound like a good idea?

Thanks for your help