It can take a few cycles for your body to normalize after you go off birth control. In fact, some women can take up to a year start to ovulating again. It is always ideal to come off oral birth control prior to when you want to become pregnant just in case it takes your hormones to regulate. Some women get pregnant right away so keep this in mind and use other methods such as barrier method if you are not ready to get pregnant right away. There isn’t a way to know how soon you will become pregnant but it is always ideal to get your body as healthy as you can prior.
See this post to find out how to increase your chances of getting pregnant.