Well, I just came across this forum as I am just getting interested in yoga.... but I would like to suggest a form of body work to you called Rolfing. It is a structural Integration modality and I have just completed my series of 10 sessions with a certified Rolfer for the exact same problem as you have described. I can see a lot of changes in my posture and there are some yoga poses that she suggested that could help me in my self-help sessions. Check in the area where you live to see if there are any certified Rolfers or Structural Integration bodyworkers that you may consult with for your issues .... and best wishes. There are solutions out there if we can only know where to seek them out.
Drema M.