I'd say it was mostly the first mile too fast. In a 5K, you pretty much can't recover from it if it's really too fast for your fitness.
"I've been following Eddy's improvement over the last two years on this site, and it's been pretty dang solid. Sure the weekly mileage has been up and down, but over the long haul he's getting out the door and has turned himself into quite a runner. He's only now just figuring out his potential. Consistency in running is measured in years, not weeks. And over the last couple of years, Eddy's made great strides" Jeff 14 Jan 2009
I think you answered your own question.....you started out too fast. Try to have your first mile be your slowest and your last mile your fastest It 's tough to hold back on the first mile....but my goal is to hold my place/pace for first mile and then pick people off one at a time....not letting anyone pass me.
Yet for the last 5k I just wanted to try the going out faster approach, and I can say I will never be doing it again!!