no gas in the tank

I had NO energy for this run. My legs have been stiff and sore since my Saturday run, and I was just wiped out! It was a measley 3.5 miles, and I barely ran it faster than if I were pushing the stroller. I'm sure that the beers that I drank the night before didn't help, but am I doing something totally wrong with my diet? I'm getting two rest days per week (sometimes three or four!). Maybe it's my shoes, too. These things have over 600 miles on them. Time to really make some changes.