To anyone who happens to find this page through a search or just by browsing:
if you have such a hole (between half a cm and like 2 cm above your "normal hole") what you should do is this
-talk to your parents. Ask them if you were born with a pilonidal dimple. Many, many babies are born with this and its a very mild defect with little or no further problems in life besides infection.
-if they know ask if the ultrasound or whatever test was done confirmed that it didnt go any deeper than a little bit.
-if they don't know, or even after you've spoken with them, you should still see a doctor. They will know best. Explain to them what it is and exactly what youve experienced with it.
Myself personally - I just discovered I have this. I've had a little discomfort there when sitting on hard floor, but I never knew I had a little hole there. I haven't seen a doctor yet but it's only been a few days since I found out. Anyway, I researched all of this and chances are, you'll be o.K.
The worst thing that could happen is you find out you have an infection and need to get it removed. Least that could happen is you find out it only goes down a little tiny bit and you just have to make sure it is clean everytime you shower. Not a big deal.
Good luck everyone, and talk to your parents and a doctor!