Missed period by two weeks

So I've had safe sex with my boyfriend but there has been maybe two times where (after a shower) he goes in without a condom for quite literally a few seconds and then puts on a condom. He's freaking out that I'm pregnant, even though I took a pregnancy test a few days ago and then another one yesterday and they both said I'm not pregnant. Is it possible something is wrong with my body? I usually have an irregular period but even two weeks missed is strange for me. Please advise!