Frustration Nation!

A year ago, I was a huge runner, had been for a good 3 years. I looked like this girl above. I loved to go running, I did a few road races and loved every minute of it, I was addicted to the runner's high, but than I started a job that had very inconsistent hours and than I started school and that took a lot of adjusting and I just feel out of routine and motivation to continue running! Until yesterday, I decided, I want to go running, I miss running, I need to go running! I strapped on my running shoes, plugged into my iPod and off I went. Until on song later when my knee was throbbing, my lungs hurt and I wasn't really looking to swell. I was looking more along the lines of this guy,
It really was one of the most pathetic runs I have ever had, but it felt good! So, this morning, I strapped on my shoes again, choose some awesome running songs and went out again and went a little bit further and it hurt a little bit less and I pushed through the knee pain. Do you have any advice on how to stay motivated or to push through the first few days of getting into a routine of running and sticking with it? I know as soon as I see a few pounds drop away I will think to myself, "I can put off running for a few days, no problem." I can't let this happen, any words of wisdom to keep me going? I'll take whatever you have to offer!