How do they do it?

In reading my favorite blogger's post today, I felt all at once inspired, awed, and sad.  She ran a marathon and felt great at the end of it.  She posted pictures of herself before and after the race, and of course, looked fantastic.  How does she do it? 

Being sick/ having disastrous things happen over the past few months has rather killed my spirit.  Just as I thought I was getting it back, I was knocked down again.  And now I'm just tired.  I feel like I have a ton of things to do, and no motivation or energy to do them.  I mourn my old self, the cute, perky, "skinny" me in the pictures I mentioned in my previous post.  It feels like she's dead. 

I know, logically, that if I get back on the horse and make myself work out as many days a week as I can manage (5-6, ideally), I'll start feeling fantastic.  But I can't seem to want it.  I just want the old me back.  I want my meds to work and I want to fit into my smaller clothes and I want my stomach to be flatter and my arms less flabby and I want to feel good about myself.  But it's going to take work, and it's not something I feel I have the energy for.  So sad.  Nevermind that I'm working full time and school started again (and I started by flunking a quiz and missing a discussion), and I'm really worried about being able to pay my bills.  Overall, it feels like life sucks right now.  I'm not sure how I'm going to make myself get out of this funk.