Spotting, 16days late but negative test?

[Dannii_mummy]

Hello, my sister is currently 16/17 days late for her AF, she started spotting light pink discharge, then few days later a browner discharge, she's done 2 pregnancy test and they have both said negative ? what can this be?
If she was to be pregnant she would be 6weeks gone, wouldn't she have a BFP by now?

 

[itsnowmyturn]

Not always. Some ppl just don't get positives on hpt, some need blood tests