Fertility

So let’s get straight to the point .. I had 3 serious relationships me & all of my bf’s always started out using protection then ended up not using protection or the pull out method .. my current bf has been nutting in me literally for the past 2-3 years & I have not gotten pregnant YET ! I’m getting frustrated 🙁 we have sex at least 3-4 times A DAY depending on our work schedule and how tired we are I also have a fertility app which tells me when I’m fertile (obviously) any opinions? We are a very young couple so what could it be ?? Not to mention he has 2 kids by his Ex .. so could it be me ?