I think the best motivation is early success. When I first started paleo two years ago I lost 11 pounds in a week just by removing grains and junk from my diet. That led me to remove other horrible things from my diet like fruit juices and to start exercising. After 5 months I'd lost 40 pounds and have kept it off ever since. Since then it's just become my lifestyle and no real motivation is necessary.
How about exercise? Have you continued to workout consistently? Even skinny people need to workout. Also, cut out the crappy food, yes but also be sure to add food with good nutritional value. My issue right now is getting outside and working out consistently.
Successfully losing weight and getting into great shape makes working out become addictive. I started working out and running when I quit smoking. Instead of gaining weight after I quit smoking, I lost 17 lbs. within three months. Now if I could just lose those last two inches in my gut, lol. I have an issue with eating; I enjoy it too much. I consume 3000 to 4000 calories per day, but because of my active lifestyle and high metabolism, my weight is holding steady right around 140 lbs. I was down to 137 at my peak which was Thanksgiving. By mid January I was back up to 145, but I was sick for a couple of weeks and unable to work out. It took me about a month to get back down to 138.
As for eating, rather than count calories, I just dumped all the wasted calories. I quit drinking soda and stopped putting flavored creamer in my coffee. I started drinking more water and now I drink my coffee black. As for food, I eat until I am full, not stuffed, and I eat whenever I feel like it. I generally eat four meals per day with a lot of snacks late at night. Breakfast at 10, lunch at 1, dinner at 4, second dinner at 8 or 9, late night snacks before bed. During warm weather months, I run five days per week, about 25 miles per week, and lift weights two days per week. I take one day off per week. During winter, I go to the gym and run on the treadmill or use the ARC trainer. If you go to the gym, try it out. It beats the hell out of any elliptical or stair stepper. I can burn 1000 calories per hour on that machine, although I usually only use it for 40 minutes, two 20 minute sessions.
After smoking for 30 years, I finished my last 5K in 22 minutes and finished 4th out of 80 in my age group. Bottom line is if you want motivation, set goals that you can achieve and make sure you achieve them. As you see success, it will drive you to set higher goals. Just don't make your goals too high so that you cannot reach them in a reasonable amount of time.