Just STOP the thought train that creates "reasons" (excuses) and debates whether or not you should exercise or eat right. When I hear myself debating and rationalizing, I call myself out on it. "Heyyyyyy.........wait a minute........" Once I realize where that train is headed, I jump right off and get back on the right track. Listen to yourself and quit thinking! ;-)
Put your left palm on the back of your right shoulder. Put your right palm on the back of your left shoulder. Now SQUEEZE really, really, really tight. Hold. Release when you 1) feel better, 2) stop crying, or 3) start smiling. Repeat as necessary.