How do I stay disciplined/motivated

Background: 6'5", male, 21, 255 pounds, average build, after a year of regular weightlifting and cardio, but without really watching my diet, dropped to 235. recently stopped working out for a month and gained back to 240. It seems like that whenever I become stressed I would eat considerably more junk food. Unfortunately my stress is due to working as a consultant with very irregular hours and also studying for GMAT. It didn't help that a 24 hour hot dog stand opened up across the street from my place recently either. My question is how do you guys keep motivated with working out and dieting, and to abstain from junk food in my situation. Its just depressing to see that after a year of work and I'm finally showing progress and a quarter of that was lost so quickly.