Vaginal Sex... how?!

Okay so I've been mastubating since my pre-teens and am currently 21. I use toys on my clit and enjoy rubbing the general area, but even when I'm naturally really wet or using a lot of lube, I still can't push more than 1 finger in! How do you even do that? Is there a bit of resistance I should try and endure?
(Ps haven't had any sexual partners yet!)