Help!

Okay I haven't had my period at all this month and I am now three days late.....I took a test last night and it was negative. I don't know if I'm pregnant and I don't know when I should take another test. My partner and I had sex on the 8th of this month and that was my ovulation date. I was 33% likely to get pregnant on the 8th. And am I testing to early?