Running out of gas...

I seem to be having this problem a lot lately. I'm doing fine for about the first 20 minutes of a run, and then I begin to just run out of energy. I'm not hurting; I don't have any stitches or cramps, but I'm just out of fuel. I'm not sure if my sugars are off, but I have a feeling it has more to do with my electrolytes. I say this because I recently began drinking sports drinks since I've finally managed to consistently run more than 30 minutes with every outing. Today I meant to take my G2 with me but forgot it. During the run today, I just pooped out! I wanted to keep running, so I'd run as far as my little legs could take me and then walk a bit. Then I'd run some more. I got home and chugged my G2 because I was soooo thirsty. Lo and behold - my energy came back! I've read a couple articles that said even just a little sports drink mid-run can boost energy levels dramatically, and I have a feeling I was experiencing that effect. Long story short, I will have to invest in a small bottle to fit on my running pack for a little sports drink or just carry the darn bottle with me. I could not believe how much better I felt. Sometimes life's problems have such simple solutions!