B12 can help to balance your hormones and can help to increase your luteal phase. What CD day are you on, and what CD does AF normally fall on?
How do you know if you're B12-deficient?
Your Dr. can order an blood panel to see if you are deficient in any vitamins. B vitamins are water soluble though, so taking them won't hurt you even if you aren't deficient, as your body will just allow you to urinate out the extra (giving you neon yellow pee, lol!)
Can't hurt to add them into your daily vitamins.