Positive then negative tests???

Aby

So I’m 5 days late for AF. I did a test Friday morning to which it was positive. Then done a CB yesterday around 4pm was negative then today done a first response around 3pm and negative too? I’m so confused. I’m a regular 28 day cycle and am never late. I’ve been constantly tired the past week or so and just feel different. Any advice? Going to ring the docs tomorrow