Positive cb digi then Negativd cb digi two days later

Hi, I had brown spotting (well when wiped) week before AF due then one day of very light bleeding (not even one full tampon) on day AF due then nothing since, did a Cb digi test three days later & was Bfp then two days later tested again with Cb digi & negative but no bleeding, still feel like I have mild preg symptoms :-/ very confused, Dr has asked me to put a urine sample in 1st thing tomorrow!