Delayed menses can be caused by a variety of reasons other than pregnancy. You did the right thing by taking a pregnancy test after missing your period. I don't think in your case the reason for the delayed periods could be pregnancy especially as your pregnancy tests have all tested negative.
Stress, lack of sleep, weight fluctuations etc. are all factors that can lead to longer than normal cycles. Hormonal imbalances, weight fluctuations, thyroid illness, polycystic ovaries etc. are also other causes of delayed menses.
I would advise that you wait for atleast 2 - 3 weeks for the onset of your periods. As longer than normal cycles are part of the variations in ones cycle lengths that every woman undergoes with age, you could just start your periods a little late this month. If the absence of periods i.e amenorrhea persists after 3 weeks then it would be okay to consult with a gynecologist or family physician regarding the same.
The doctor will examine you and will probably advise certain hormonal evaluations, ultrasound examinations to determine the cause of delayed periods. The treatment of the same would largely depend on the underlying cause but would also involve hormonal treatment with progesterone containing pills that will help to induce a withdrawal bleed.
Most of the times such delayed cycles are just the body's reaction to our stressful lives and generally the cycles regularize with time. Persistently irregular cycles (longer than 6 months ) however definitely warrant a medical opinion.
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