Sounds like it could have potentially been a boil. The oily blood is usually a pus/blood mixture and could have also been a pimple that was infected. Odd place for a pimple I know, I get them in my inner thighs all the time though. Both boils and pimples.
If it was near the top of your ( I don't know how else to putt it sorry...) crack, then it is probably a pilondial cyst. Look it up.
are you sure it wasn't a hemmoriod? because I have one of those too! if its a pimple I would of popped it..lol
I have had a bump the same location you described for as long as I can remember. I know it is hereditary, because my sister has it and so did my mom. I think I was told it is a cyst. Mine remins painless unless I am stressed out or have gone #2 too many times. It was also irritated a lot when I was pregnant. Mine has burst open a few times, but then reforms and is solid again. You may want to check with your doctor to be sure, but that's what it sounds like it is. Good luck.