I have tried several different diets- weight watchers, slim fast, atkins, cabbage soup and have had limited success. I have some family members that are using Medi Fast and have lost about 40 lbs in 4 months. Thats the kind of success I would like to have. Does anyone have any first hand knowledge of Medifast?

The reason Medifast works is because your calorie intake is restricted. We all know that if we lay off the fast food and late night snacking we will stop gaining so much weight.
Barring some rare medical condition diagnosed by your doctor, the answer to your failure is simple: you are eating too much and are not getting enough exercise.
I am so tired of people complaining that they just “can’t lose weight!” Stop complaining, take responsibility for your situation and solve the problem! It is easy. Go to your doctor to make sure you are healthy, then get advice from him/her on what you should to to get healthier. Those fad diets out there are not healthy and are not long-term solutions to your problems.
Your problem is lack of self control and laziness– do you really want to treat your body like this? You owe it to yourself to do the best you can to get (and stay) healthy– YOU ARE WORTH IT!