Hello dear
understand your concern
Most common cause of delayed
menstruation in sexual active women is pregnancy. Pregnancy test will give positive result 10 days after missed period. Do not worry.
Better confirmation of pregnancy is done by blood HCG and USG scan.
Cause of negative may be as you did very early. Yes there is no more HCG at 8th day thats why it was negative.
Faint line may be occur in very early pregnancy, ectopic pregnancy, hetrophile antibodies, Ig A deficiencies, etc.
Also note other causes of delayed period: sudden change in life style and dietary habit,
thyroid disorder,
ovarian dysfunction,
hormone imbalance, adenomyosis, leutal phase defect etc.
If pregnancy is not there , you can do following investigation if period will not come: USG, PAP smear, full hormonal assay,
endometrial biopsy etc.
You can also use norethistrone to induce bleeding in absence of pregnancy.
Hope this may help you
Best regards
Dr. Sagar