Oh I'm sorry, I misunderstood.
No they won't help you get pregnant. They will help you get healthy/ier to get pregnant and help with the baby's nutrition once you do get pregnant, but they won't help you get pregnant.
Since your cycle is not regular, it's hard for anyone to calculate when you would ovulate. Try one of the tracker or apps. Mycycles is a great help.
I asked could prenatal vitamins help me get pregnant?
Prenatal vitamins will not help you start your period. There are many ways to determine when you ovulate. You can chart your temperature each day in the morning before you get out of bed. When it dips a bit, you are getting ready to ovulate. When it spikes, you have ovulated. You should have sex around the dip in your temp.
Also, medhelp has trackers and apps for this. You can find them under the Health Tools at the top of the screen. Good luck!