Completing my FIRST 5K... and falling down

This past Sunday, my husband and I completed our very first 5K! We finished in 1 hour and 1 minute, which means we walked just under 20 minutes per mile :) 20 minute miles were my goal, so I'm quite proud of our time! My husband, on the other hand, became pretty competitive once the race began.
I had no idea how many people take these 5Ks super seriously! About 75% at the race were runners and most of the others were serious speed walkers. My husband and I walked at a moderate pace and were towards the end the entire time. He really motivated me because he was TICKED being so close the last people. I, on the other hand, was just proud of us for getting out there and giving this whole 5K thing  a try! I don't think I'd have been brave enough to try it 40 pounds ago!
I didn't fall down during the race. And I didn't immediately afterwards, either. In fact, we went to the gym and lifted for a half hour and then came home and went swimming. We were VERY active for the first half of Sunday. And then I realized I had been doing all this activity without putting fuel into my tank and I was starved.
And I ate my normal lunch. And then I ate a few chocolates I'd been saving for a time when the craving hit and I need to satisfy it. And then I ate Laughing cow cheese and crackers. A lot of them. And then for dinner we ordered pizza and I ate three slices! It was a terrible binge. And seemed to negate all the sweat I'd shed during my hours of exercise.
But, it's over with and I must forgive myself. I must let go of the guilt. I'm truthfully having a difficult time with this. I don't feel badly when I plan and chose to indulge in a meal that I know is going to have extra calories. But this Sunday binge was NOT planned. And I've been allowing myself to dwell on HOW FAR I have to go and how much work it's going to take to get there. Today I feel like, man, I have 50 more pounds to lose and six months to do it in. Is it even possible? I know it is, but I know that I have to stop making huge mistakes like the ones I made on Sunday if I am going to reach my goal of 200 pounds by Christmas. I know I have to work out two hours a day three or four days each week, and do my 45 minute DVDs on the other two days each week. Frankly, it's making me tired just thinking about it!
And I'm still wrestling with some anger. Why, why, why is it SO much harder for me to lose a pound than it seems to be for some others? Why can I work out and write down every single thing to pass my lips and still only lose a half pound in a week? Or worse-- not see the scale move at all?!
I know it's a waste of time to even think this way, but the devil leads me down this path sometimes.... I see what other people eat and I see what kinds of exercise they do. I work out like a beast! Every time I leave the gym, I am COVERED in sweat. Disgusting sweat-- my ears and nose even perspire. That's how much intensity I put into my workouts.  Somewhere metabolism and genes kick in and I wonder how I wound up with such crappy ones!
Enough complaining! I guess I need to find another 5K to train for!