How to get pregnant fast?

Anyone has a difficult time getting pregnant the second time around. Currently, 25 years old trying for baby #2 for a Lil over eight months and nothing yet! My first child will be six soon, and I don’t want to wait, so there won’t be such a huge age gap between them. Any advice on how to get higher chances of getting pregnant soon? P.s took a round of P.I.O (progesterone in oil) shots for a fertility boost.