Illness - A sudden, short illness like fever, cold, cough etc. or even a longer illness can delay your periods. This is usually temporary and once you recover from the disease, your periods get regular.

What illness can delay a period?

Periods can also sometimes stop as a result of a medical condition, such as heart disease, uncontrolled diabetes, an overactive thyroid, or premature menopause.

Why does being sick delay your period?

Illness. Certain illnesses, such as a cold or the flu, can also stress the body and impact ovulation, and, as a result, your period. If illness around the time of ovulation caused you to skip a period, it will likely reappear as normal next cycle.