Late Period Negative Test HELP

My period is late by 2 days. It's never late even when I'm stressed. I took a test 2 days ago and it was negative. We are ttc so I know when I ovulated. And I know when we had sex. If its the day of my missed period like it's supposed to be when you test why would it be negative? Unless I'm not. Has anyone else took a test on the day of their missed period and it be negative but still be pregnant? I'm going to retest obviously but I would like an idea so I'm not dissapointed. I'm so confused. Need lots of opinions please!