Mere absence of menses does not confirm, and moreover you have already undertook a few pregnancy
tests which are negative. It could be a case of Amenorrhea
(absence of menses), to confirm that you need to consult your gynecologist who could examine and ascertain the cause of absence of menses. A hormonal
Assay could be advised with USG abdomen to study your case better.
Do not panic just consult your Gynecologist for further assistance. In the mean time kindly be specific with your diet have healthy food, add physical exercise to your daily routine.
Wish you health and happiness