Pure luck or Not that fertile

So I was wondering if my husband and I are having great luck or do I maybe have some fertility issues... we strategically plan and know the days he can finish inside (couple days before period and 1-4 days on period). We have had much success with no surprise pregnancies with these calculations. Im curious though as I know and hear of many women getting pregnant when their spouse finishes inside at any time of the month including before and during period! Obviously were not trying to get pregnant but I am curious since he has finished inside many times on my certain days if we really are timing it just perfectly or could I have some infertility issues?