How to motivate yourself?

Ermm I find I'm slacking off and I'm procrastinating. I know why and what I should do but I don't seem interested. Like I'm gaining some weight and I know it's gonna be a problem later. I have math homework but it's not a big part of the grade. Don't tell me to get my **** together or anything. I don't skip school because I know I have lots of friends at school and my mom would tan my hide (she's really strict). I know my responsibilities but I just don't feel like doing it. I know why I should do it but I just don't see the real value. Someone told me that inspiration is like sitting on a push pin. It makes you jump and acually do something. But to me inspiration is like sitting on a push pin too. I jump up, rub my butt. Get interested for a minute then go back to sitting back down. How can I motivate myself?