I am 12 days late which never and done one test with faint blue line and two more negative what do u think?

Pregnancy unlikely: But, one can retest after 1 more week. Generally, pregnancy is the most common cause of a missed period if a woman is having sex. If not pregnant, other causes of a late or missed period include: excessive weight loss or weight gain, increased exercising, emotional stress, having an illness, traveling, medicines (especially birth control pills), hormonal disorders, etc…