You can get pregnant right away. You can even get pregnant on an irregular period. The big question is why is your period irregular? If something is making them irregular and you're not sure what I would go see a doctor because something could be going on that is preventing you from getting pregnant.
No ive never been on any type of birth control,im just always irregular but as of october it comes on same day each month
Are you on birth control?
If so I say maybe wait 3-6 months then stop taking thr pills and try on your own.