You should measure your body fat index, which will allow you to accurately calculate your lean tissue mass, your daily caloric requirements (so many calories/pound of lean tissue + BMR) and hence, your nutritional needs.
I just bought a caliper fromm a local healthcare store (only one store on an island of 140,000 had one). It's called the "Fat-O-Meter" and it's made by Novel Products.
It comes with a booklet with instructions on how to get measurements using a skinfold caliper. Using the data, find your caloric requirements, subtract 500-1000 calories (or 20-30%) then divvy up the calories into meals.
Eat 5-6 small meals throughout the day, spaced 2-3 hours apart. Eat your biggest meal in the morning, and your smallest meal at dinner/evening. Eat some Protein with every meal, and carbohydrates. Don't let Fat intake go above 30%. Eat healthy food. Plan your meals days or weeks in advance. Plan your day ahead and figure out when you can incorporate a meal (2-3 hours). Every 4th day, eat more than you calculated, even over your max calories. This will prevent the body's starvation response kicking in and slowing progress.
Exercise regularly. Cardio and weight training, alternate days. Try high intensity interval training (15 secs running max, 60 seconds jog, repeat). It burns more calories. Constantly measure your progress (remember the caliper?

) Make sure you are not losing too much lean tissue. 1-2 pounds of fat can be safely removed from the body per week. Any more than that is guaranteed to be muscle or water. If you hit a plateau, change your exercise routine, the type of exercise, anything that works. Alternately, if it ain't broke, don't fix it.
As for the motivation thing, I can't help you with that. That's up to you.