RGR, after many failed attempts, I finally achieved something similar- I lost 60 lbs in 7-9 months.

The attempt that finally succeeded was different in that I committed myself to initially do only one simple thing- walk every single day for 3 weeks. I didn't worry about distance in this first 3 weeks. I focused only on starting the habit. So that meant medium walks around the neighborhood most of the time, but sometimes longer walks and sometimes only 5 minutes around the block! I didn't care about having enough time or what time i got home at night. I just made sure I could say to myself that I genuinely "walked" today. That 5 minute walk around the block on those toughest days counted, and that was critical!

After 3 weeks the investment (habit) was in place. Also by then I was starting to feel the positive changes in my body, and THAT, plus the habit I just started, took over and it was much easier (self motivating, rather than people telling me what to do) to eventually move on to eating better and more aggressive exercising (for me, eventually running.) I did this on my own- letting one thing lead to another- but I owe it all to that initial 3 week investment in starting the new habit.

(My Chinese Doctor gets credit for this simple plan.)