Why do I have this and how can I get rid of it?

[bro123lol]

I'm an 16 year female. And over the last couple months I've been noticing redness right under my bottom lip and then it goes to the corners of my mouth.It comes and goes and I just can't tell why I have it. IT doesn't burn it doesn't itch. It is very red and noticeable. I don't want this on my face where everyone can see it. It probably has happened to me twice over a 6month period of time. at first it is very red and irritated then it becomes very dry like flakes will literally fall of my face. Then right now it's been a week since I've had it and the corners are a dark brown kind of color.  It isn't very noticeable but if you look closely it is. I play a lot of sports. I may not drink as much water as I need to. AND I don't wear sunscreen which Could definitely play a role SOMEONE PLEASE HELP !!