What happened??

I was enjoying our married life with my husband. Enjoying our intimate times. Boy they been good! Then I started to notice my breasts were sensitive and painful. We haven’t been preventing pregnancy but we aren’t trying. I was due my period in few days so i was planning to monitor that. After day 3 of my missed period I did a test. It was faint positive. I couldn’t believe it so I did 3 more different brands. All positives. I was excited then day 4 my period came. What the happened. I had a blood test with my Dr. Later that eve and she told me my test came back negative. She then did a really sensitive test, BhCG, my results was just below the recognised threshold for pregnancy. Did I miscarry? Was this a what is called a chemical pregnancy. My Dr doesn’t seem to believe I did my initial tests which I know I did. Has anyone been through this? What happened??