hii karthi, Your presenting condition is OLIGOMENORRHOEA and One thing you have to know clearly that MISSED PERIOD is not a single reason of pregnancy,it can be occurred in other conditions like PCOD, HYPOTHYROIDISM, Mental Stress along with Vigorous Exercise, Anorexia etc. So you need to investigate properly. If 5 pregnancy test are negative then do a USG, Thyroid function test, FSH/LH, Blood prolactin level to detect underlying pathology and consult your gynaecologist. All the best.