Keeping motivated

How can I stay motivated to work out every night/morning? Or how I can't forget either.

I sometimes get into it for a week or two and then I start quiting againg. I've tried alarms and setting time for it, but even then I'm like, I don't feel like it.

How can I change this?

Also I get hungry often, but I think about wanting to exercise instead, but then I never end doing either one, or I give I to eating.

I'm 17 years old and I don't have an eating probelm.....that I'm aware of at least.