Hi welcome to healthcare magic
Delayed periods or oligomenorrhoea is diagnosed if there is a space off 35 days or longer between periods.
It can be caused by a number of factors including:(1) stress either physical or emotional (2) excess or extreme physical activity (3) inadequate diet (4) abnormal levels of thyroid hormone (5) abnormal levels of other hormones such as prolactin
(6) PCOS- polycystic ovarian syndrome
which is a condition with cysts in the ovaries, infertility
, abnormal levels of male hormones, irregular periods
and insulin resistance
.(6) pregnancy however you stated that you had a negative test (7) perimenopause
You should consider visiting your doctor for an assessment, he or she will take your history and perform a general and gynecological examination.
I hope this helps