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
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.