In reply to plyometrics:
Have you tried self myofacial release?
The basic technique is you find the sore spots in the tight muscles, and apply a constant pressure, not releasing until you feel the pain start to ease off, which usually takes about 30 seconds. Sometimes you'll feel a burning sensation before it starts to ease off - alarming at first but all part of the process. Doing it regularly really helps reduce pain and speed up the gains in range of motion from stretching.
This is a great tool for getting into the the lower back, buttocks and hamstrings:
https://www.amazon.co.uk/Physiomed-THE-ORIGINAL-BACKNOBBER-II/dp/B0036LQOQE...
There's a chap called Kelly Starrett who has some free stuff on youtube, and a book called Becoming a Supple Leopard, available from all good book stores for those who don't like copyright abuse... has some good ideas for promoting movement of the soft tissues with lacrosse balls, broom handles, and all sorts. Be prepared for real pain though... when you start adding movement on top of the pressure it can get to the point where it makes you want to puke.
As they say, no pain no gain though... I put myself through a daily hour of self-torture for about six months, and haven't had to enter a phsyios office in the three years since (before that I'd got to the point it would need treatment two or three times a year).
I worked around pretty much all the soft tissues from my lower back to my ankles, but paid particular attention to my short and tight piriformis, psoas and hip flexor muscles, and the erector spinae muscles that were overworked by my poor posture.
Another tip I got from that physio - when trying to correct pelvic tilt in your posture, you need to think about the thoracic spine as well - if the pelvis tilts forward then you also tend to hinge backwards around the bottom of the ribcage to stay in balance... trying to correct one without the other is doomed to failure.
Hope that helps