Weight Loss

I am 3 years post op and have lost slightly over 100 lbs.  I am not losing weight anymore and I would still like to lose another 50 lbs.  I have had two surgeries in the last year for knee replacements.  One surgery was in September 2010 and the other one was in June 2011.
I walk 45 minutes each day.

Can someone advise me of what to do?

Have you thought about meeting with a personal trainer to see what else you could incoporate or change up to kick start your body into weight loss mode?