Excuse me if this has been said or posted before, but I recently discovered this.
If you don't mind a little cheating, open your Cheat Tab and type,
testingcheatsenabled true Invite your vampire (the one who'll bite your sim) over. When she/he gets to your home
drag the relationship bar all the way up and
Ask to Turn, your sim will get the moodlet, which last three days of waiting.
Delete the moodlet by pressing Ctrl+click on moodlet. The moodlet should disappear and your sim should become a vampire, right there. This also works for pregant sims.
I honestly hate waiting the 3 days.
