Confused

I took a few first response test about 2 weeks ago and got a positive on three test from different boxes. I’m now roughly 13 days late.

I went to the doctor about a week and half ago and the test was negative, and today I took a clear blue and it was negative.

Why did I get three positives and now negatives?

I been nauseous and been having heart Burn but no period since April 14th.

So I guess I’m not pregnant? Or should I ask for a blood test?