just go to the doctor. It's probably any easy solution.
Oh and FYI, it's worse when you wait... The results or condition is usually worse. My mom had Melanoma (deadly skin cancer) and died within 6 months because she didn't address the symptoms until it was too late. I'm not trying to frighten you, i'm just telling you my experience with a loved one that just kept putting off seeing someone that could have helped her.
When i was a young lad i had an allergy to milk...
About 30mins after having any i got really bad nose bleeds...
So i guess it could be an allergy, although given that it's started now and not when you were cracking skulls i'm guessing thats the least likely.
Chances are there is a little bit of blood vessel damage inside your nose that can probably be fixed in a quick and painfree process called Cauterization.
I had mine done and after the 3rd or 4th time i eventually got a doctor skilled enough at the process for it work.
Ask your doc about it... it's certainly nothing to panic about... unless of course there are bits of brain in the blood! ;)
Take care!