help me

I took a Plan B pill on October 24th and my period still hasn't arrived... when I took the pill I didn't bleed, not even a spot.
I went to a gynecologist a week ago and she did an eco where a possible fetus appeared; she told me it was very likely a pregnancy. She gave me a urinal pregnancy test and it came out negative, but said it was very likely not guaranteed I wasn't because it was possibly too soon to tell. She told me to take a clinical pregnancy test in ten days if I still hadn't gotten my period. I couldn't wait so I took it that same day and it came out negative, but I have yet to get my period and I'm incredibly scared and confused. If anyone may help me... please, I'd appreciate it.