Need an option....

Hello ladies. My cycle was suppose to start on 7 May.  On 9 may I thought it was starting my cycle but it only turned out light spotting (using only one tampon). The next day nothing. I have spotted or bleed since. I've done several hpt and all BFN. I even did a blood test also negative. The nurse told to wait and see what happens next cycle. I'm scheduled for an ultrasound next week for an unrelated issue. I'm praying this ultrasound will shed light on what's really going on. Has this ever happened to anyone? Could you have negative urine and blood test and still be pregnant? Thanks in advance.