Extremes

Why do I feel the need to go to extremes?  When I exercise I never feel like I've done it enough.  When I want to start a diet I become obsessive.  Then because I get obsessed with the calories, I just don't eat.  I know that is worse for me.  When I do eat my body holds on to all of the calories I consumed not just what I need, thinking that I am starving.  No matter what I need to lose this weight!!!