I think any time you push yourself to a new level of something you're body is not used to, it's going to respond with exhaustion. It does seem that with your history of other events, it shouldn't be so severe, but it could also be that your race, in addition to your life events .. is sucking the life out of you more so than it otherwise would.

I would listen to your body and give it the rest it needs as much as possible. Maybe skip some workouts if not all of them for a bit. The better you recover from this race, the better you will do the next.

Congrats on your first race, though.