Temporary Detour?

My goodness, the last two weeks have felt like an epic fail. I want to turn it around, and I'm just not feeling motivated. Help!

My diet slipped and I didn't make it to the gym for a week, and when I got on the scale I was back to my starting weight. Worse, when I got on the machine at the gym, I was panting like I'd never worked out. I worked hard to achieve so little, and with one bad week I lost all the ground I'd gained.

I was so discouraged I spiraled into even worse habits this week. Because that makes so much sense, right?

My body feels terrible, and I'm grumpier and more irritable than before. Yes, I'm experiencing a higher-than-normal level of stress. I've applied for a new job, a process that started in January and finally reached the interview stage a week ago Wednesday. I'd been hoping to hear back within a few days, but the person in charge of hiring was traveling all last week, so I'm crossing my fingers for the upcoming week. It really is cruel and unusual treatment to stretch out the hiring process this long, but they're historians, so maybe they have a different concept of "a long time." And I really, really want this job, so I will wait as patiently as I have to.

But it's not like getting this job will completely change my eating and exercise habits, though they do have a rule of no food in the office (the office is in the same building as the library and archive, so food is a big no-no). Right now I'm surrounded by snacks and eat primarily at my desk, so that would certainly change. And my office would be on the 4th floor, so I could take the stairs more.

Anyway. I'm frustrated with myself. Why is it so hard to translate knowledge into action? What is the key to making it stick?