Re: pilonidal cyst maybe?
It sounds like you may have a boil of some kind that needs to be drained and you may need antibiotics. Don't know since neither me or you can see it very well.
But a pilonidal cyst is a cyst that involves the base of the spine and as a cyst is not infected but if/when they become infected, it's treated much like a giant boil and drained and cleaned out.
So either way it needs to be seen and treated. I've had boils on my butt and I've had a pilonidal cyst removed and personally, the pain before they are drained is worse than the pain of them doing it or afterward. Don't worry and get it treated.
And who knows, maybe it's not an infection at all and is something you can leave alone. But only your doc will know.