Semi annual periods

Hey ladies!

I’ve had a regular period cycle all through my life until recently. I had my last period June 26, 2017. I have had sex once since May and we used protection and the male didn’t finish. I’ve been to the drs regularly to test if I was pregnant and after 10 tests all negative. I still haven’t received my period. Ive had Pap tests, ultrasounds, blood taken and no one can figure out why I haven’t received it... anyone have similar experiences?!