A bit confused ?

I used to have protected sex two years ago 2016 April-Aug. until me and my bf decided to try without one, I know the consequences and all about being pregnant for not using protection. But it’s now Aug 2018 and we’ve haven’t been using protection ever since, but I’m confused as to why I’m not pregnant. He pulls out, but that’s about it, I’m not on BC, but I do have keloids on my ovaries lol. Can someone explain as to why I’m not pregnant yet? I’m 19 btw, so has nothing to do with age.