Was he running around anymore than usual?
I used to get them A LOT and they would last for sometimes up to or over an hour, the Dr's could never seem to explain WHY i got them.
I found if i was HOT or had been running around a lot i would get them, if someone accidentally bumped me on the nose etc.

It might not be something to rush off to the Dr's for but i would mention it next time your there and see what they think, IF though they are lasting long periods of time and not clotting properly then it wouldn't hurt to get it checked out at the time.
I had my nose quarterised (sp?) when i was younger but started getting them again when i was a teen

GL with it all, it's not a fun thing to go through, especially if you have to pull out those nasty little clots