I too had problems losing weight and keeping it off. 2 1/2 years ago I tried loseit.com and lost a pound a week (roughly) for a year and have kept it off. I went from 210 lbs. to 160 lbs. and my knees don't hurt anymore and I don't take glucosamine any longer.
Lose It! is a simple free app that runs in a browser and on IOS and Android devices.
There is also MyFitnessPal.com which is similar.
Either one will get you the weight loss you want if you are serious enough to stick with a weight loss and exercise program.