Please get an ultrasound of the pelvis or the transvaginal ultrasound
, that would help in confirming the cause and rule out pregnancy
You could also get a serum beta HCG
test done to rule out pregnancy.
Repeated negative HPT tests say that the chances of you being pregnant are very less.
It seems like hormonal
imbalance, and you should get your periods soon.
You could consult your doctor to give you pills that can cause withdrawal bleeding, provided you are not pregnant.
Hope this helps you.