Missing period month 2

In July (after my period) I had sex while I was ovulating (according to the <a href="https://play.google.com/store/apps/details?id=com.glow.android">glow app</a>)  and one more time just before my period was due (in August) 
Both times my bf and I did not use any condoms but he did pull out. 
I did not get my period in August and September is almost over and I still have not gotten my period. 
I took a urine test and both the at home ones and the one at the clinic says negative. 
I'm about to make an appointment for a blood pregnancy test, but I want to know if anything like this ha happened to to anyone else.
Have you gotten a negative pregnancy test with missed periods? Or have gotten a false negative when you actually was pregnant?