Will I ever?

Cora
Hi all, I have been with my partner for about 2 and a half years. 
We have been having unprotected sex the whole time and I am on the pill. 
No we are not trying, but not really preventing either. 
I have at times forgotten my pill, or taken it not at the same time. 
It has just come to me that am I just really lucky haven't fallen pregnant yet or could there be an underlying issue? 
(I would still be incredibly happy if I were to fall pregnant anyway) 
Thanks x