As stated, a little difficult to say without seeing your physical game and approach. I also highly agree with Charlest on seeing a physician or therapist to ensure not any extensive damage has already been done.
My personal teaching and method regarding leverage and balance is that the amount of centering the sliding foot to torso or chest for proper balance is relative to the bowler's physical lift effort. Seeing as how you're a "no thumber", I'm "assuming" you turn the ball fairly well or strong at the point of release, therefore necessitating a stronger balance position with your sliding foot/leg.
What I mean by this is that strokers or those who don't impart a lot of lift at the point of release do not need to have the sliding foot as centered to chest or torso. It can be off centered to the left some or even a lot depending upon physical attributes and varying strengths of the individual. However, if you utilize a fair amount of muscle effort to deliver the ball, it would help to have your sliding foot beneath you and centered vs being off to one side.
No different then the police drunk driving test, lifting one leg while you're standing upright. We should feel some need to either extend our arms outward in order to balance ourselves or we should feel the pressure being applied to one leg while it is trying to support the entire body weight while not being centered. We aren't built like flamingos...
Here's how you guys can test my theory. For those of you who fall off your shot after you deliver the ball, try a few shots reducing the lift effort physically (don't throw as hard or turn as much) until you don't fall off. Once you can do this, that is the "allowable" amount of lift effort that you can apply for that particular finishing position that your sliding foot is in. If you want to increase lift, start getting your left foot more centered towards body or chest and this should help you also not fall off as well. Hope this helps some...
