Possible pregnancy after negative blood test?


Has anyone gotten a positive pregnancy test after getting a negative blood test? I got a blood test 6 days after my missed period that was negative. I had cramps two days before my period was supposed to start than nothing. I still haven’t gotten my period and am at 15 days late. Now my nipples are very sensitive and I have been getting headaches. Other than that all normal. Is it possible the blood test was done too early and I could be pregnant? So irritating.