Three years ago I lost 99 pounds. I found that setting exercise goals that I could not get out off was a good motivator for me. For instance, after I lost the first 30 pounds, I signed up to do a 3 day charity walk that was 60 miles in 3 days. I HAD to train for that or I'd kill myself when the actual walk came. It helped keep me motivated. I walked every mile of that walked and loved it. After that, I signed up and paid for a hiking trip to Kilimanjaro in Africa. (Once you pay there is no going back) 5 months later I hiked up Kili with 3 of my friends and I was the only person to make it to the top. I know these are extreme and costly but now I plan smaller hiking trips to Yosemite, Bryce Canyon etc so that I keep going.
Find a physical activity that you've always wanted to do and get started!
Whenever you get down on yourself and can't see the end remind yourself that you are in better shape now than you were before and that counts.
Good luck! You can do this!