Had Concussion Previously. Now, Had Nose Bleed After Heading While Playing Soccer. Due To Temperature Or Dehydration?

Hi,
So four weeks ago I got a mild concussion and was out of my sport (soccer) for 2 weeks. I played contact for 1 week, then our season ended so for this past week (the 4th week) I have just been running and such. Today I was playing around and we played a heading game. It was the first time I headed it since the concussion. About 2 hours after I stopped heading, I started getting a nose bleed. I used to get them very often as a child and they would gush blood for a relatively short amount of time. But this is a consistent little dripping. So its not like I have to always have a tissue on my nose, but I have to blot it every so often. I'm not really sure if it's my head or if its the sudden change of temp the past day combined with the fact that I am definitely a little dehydrated.