You are suffering from irregular delayed period (oligomenorrhoea). There are several reasons like ovarian cyst
(most common), hormonal
imbalance, thyroid disturbance, stress/ anxiety, psychological factor, irregular diet habit, over wt or loss etc.
As your HPT & blood test
are negative, then possibly you are not pregnant. Here, you need to undergo one USG scan & other hormonal tests to pin point the diagnosis. After that, you can consult with gynecologist for suggestive measures.
Take healthy diet with iron supplements
, control body wt, avoid stress, take sound sleep. All the best.