What Does A Red Indentation At The End Of The Tail Bone Indicate?

I am 16 year old female who is not sexual active but partakes in lots of exercise including running and soccer. I am 5',5.5" and weigh about 135. I noticed that theres a section of skin at the top (my) left side of my butt crack right where the tail bone sticks out that was producing a clear liquid. Upon further inspection i found that in was red-ish and slightly indented. It looks chafted but causes no pain unless directly pressed on. I also noticed that i could see what looks like the outline of a vein. Im afraid the skin will break through entirely and the vein will be exposed. What is it and do i do?