I'm sorry for your trouble- what a hassle! I hope this doesn't sound like Friday afternoon (or whatever) quarterbacking, but I hope you felt all over inside the tire before putting in the tube and remounting- you should have felt the nail then. Also, I'd recommend investing in a boot (~$3 for a pack of several) for the future when you have a slice or gaper in your tire through which an inflated tube would pop. Folded dollar bills sometimes work too, but as cheap as they are, boots are a better choice.

I'm still scratchin' my head to figure out how this happened. I hope it resolves quickly for you!