Both my nephews experienced this while growing up, right around that age too, 13-15ish...
They both were seen multiple times, we had a great pediatrician team & they are both fine healthy kids.
We thought:
Low iron? Watch the diet, up the red meat, stay healthy.
When we think bloody noses we think my cousin S, she's diabetic, juvenile diabetes runs in my family & we worried about it with all the kids but they are all fine, like I said.
Migraines? We get them, is it a part, who knows, could be?
You can talk with the doctor and let them know, they'll run some basic tests 'for peace of brain' (Major League Movies, lol sorry) Peace of mind!
~My oldest just turned 13 & the stomach & headaches have started, only one bloody nose so far in his sleep. I think it might just be a thing to watch and know about for some? I'm not really sure, I just know it's shown up as a pattern in my family.