Hello, 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.