Someone told me about this story but couldn't remember the title. She remember one from years and years ago where Buffy thinks Spike has been feeding because he's being so sneaky (and she sees blood somewhere maybe?). Turns out he has taken in a very pregnant girl who gives birth in his crypt and he is trying to care for her and the baby (while being relatively clueless, obviously, about how to do it)

That sounds like Stars In The Bright Sky by Lilachigh. It's a great story!

http://www.dark-solace.org/elysian/viewstory.php?sid=1404