You have tested twice and its not possible for the pregnancy
test to be negative at 3months if you are pregnant.
Missed period could be due to some other reason.
You need to get an ultrasound
abdomen to rule out the possible causes. If normal, then you can use progesterone tablets
for withdrawal menses.
The possible causes of missed periods can be stress, anxiety, polycystic ovarian syndrome
, ovarian cysts.
A gynecologist would do the required tests as per your physical and internal examination findings.