had sex last month while I was fertile and ovulating ...

I had sex last month while I was fertile and ovulating according to a calendar. My period was may 14 th through 19th. I was suppose to start my period the 4th this month and I never did. I'm never late on my period.I keep track of my period by using a calendar app. I took a pregnancy test Saturday and it said negative. I also took it at night. They say its not normal to have periods every like 20 days. But my periods got like that after I stopped my birth control in early April. Could it be too early to test for pregnancy? When should i test again? Could it be pregnancy? My husband and I have been trying and really want to be. Any suggestions?