I don't mean to worry you, as mentioned it could be something fairly simple like a blade of grass up there or worse like a bone or something in his upper throat. It oculd be a scrape that just isn't healing fast.
But when I worked at the vets office, about 90-95% of dogs with nose bleeds all had cancer in the nasal passage.
Gosh I hope its not that, I hope its nothing serious.
I wish yous the best of luck!
keep us posted.