Cant Seem To Keep Myself Motivated?

well i have been trying to loose weight for a while but haven't tried hard enough, so now i have been asking people how to speed up my metabolism and eat healthier and exercising and ive gotten some great answers, ive even looked at some great diets, everything has been opening my eyes and its great but, i just cant keep myself motivated, like for the past few days ive been doing 50-100 sit ups at night, depends on how lazy i am, and i have cupboards and my fridge full of healthy foods and no matter what i even remind myself not to have a t.v dinner or pop tart, but i do anyways because i tell myself its just one thing whats the harm than i regret it. Long story short, i need some motivation, anyone have any stories (btw ive even drew pictures and notes of criticism and its not working..)