How does this happen?

I was doing so well last year. I had not only lost a good amount of weight but my strength and flexibility had increased tremendously. But then I started school full time while working full time. I stopped working out and caring about what I was eating and of course the weight came back and my body is no where near the strength it was. So today I want to start again but it is so hard to get moving. I guess I am just venting and hoping for some encouraging words. Happy New Year to you all!!