four positive pregnancy test but negative urine at the doctor?

Af should've arrived the 7th I started testing on the 8th with faint positive again the 9th it was alot darker. I went to the doc for comformation on the 11 but they told m my urine test was negative. I went straight home and tested on first response and it shows positive imeditally. Today is the 12th I took another Fr digital this time and it says positive too. wondering why the doc told me my urine was negative.. as anyone else had this happen?