first, get at least 45 minutes of hard exercise per day. without the endorphins naught will help.
The rest is just part of the game
If you can't stand the heat - get out of the kitchen.
14 hour days are not uncommon in startup world. I know there's no one answer to the problem you highlighted. I myself have been in similar situation multiple times and what really worked for me was to force myself to plan my day better, delegate, take a quick break...even if it means spending time with family, watching a movie or just stepping out for a walk/jog or run! Hope this helps.