Am I pregnant?

So I had my last period the week of Feb 28th to March 4th. I took a test March 5th and it was positive. I made an appointment with the doctor on the 13th and took a test there and it was negative. The doctor still seemed optimistic and said it might just be a little early and to wait until I miss my next period. I'm expecting that to be around April 3rd. Has anyone else had a similar experience and what was your outcome? I'm not sure whether to assume I'm pregnant or not...