Help after an ultrasound

I have been for an ultrasound today for various investigations (TTC for 20 months), it’s my period due date today and the radiographer spotted a black dot on the image in my endometrium, she asked if I thought I was pregnant, I said no but also suppose I could be... she said it’s likely but could also be a follicle... I’ve got mild/intermittent period like cramps in my lower abdomen but I really thought there was a chance! Took a test and BFN... anybody out there had anything similar... what was your outcome? Many thanks in advance