How can I naturally lubricate?

First off, I’ve been sexually active for 3-4 years already. Obviously on and off due to break ups, new relationships & as of now, a fwb. He’s much bigger than I’ve been with and sometimes it hurts but I like that lol. Anyway, I’ve noticed that it’s hard for me to get wet even though I’m the one who initiates sex. We’ve done foreplay, he ate me out which was something that I hadn’t had done since my first real relationship back in 2013/14. Once it comes down to the actual penetration though, I can’t get wet enough. Idk why /: