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.
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
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.
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.