Pregnant?

So we have only been ttc #3 for a month... always caught straight away before. Taken numerous tests over the last week. Period has been a bit irregular the last 3/4 months. But I think its due today. Anyway, took a clearblue yest morning.. negative! So just waiting for period to start... or not. Could I still be pregnant with a negative test yesterday? It was an early detection test so would have thought the result would be pretty accurate? Sorry for the long post.... the waiting is killing me!! Aaargh!!