Stress or Weight Change: A short-term delay in menstrual cycle can often be attributed to stress, significant weight gain or loss, or changes in exercise routine, which can disrupt the body's hormonal balance and affect ovulation.

Hormonal Imbalance: Conditions such as polycystic ovary syndrome (PCOS), thyroid disorders, or hyperprolactinemia can lead to irregular menstrual cycles, including short-term delays.
Infection or Inflammation: Pelvic inflammatory disease (PID) or other infections can cause temporary disruptions in menstrual cycles.
Travel or Lifestyle Changes: Changes in sleep patterns, travel across time zones, or other lifestyle alterations can temporarily affect menstrual regularity.

Pregnancy: Although the patient is not on oral contraceptive pills (OCP), pregnancy should always be considered in the differential diagnosis for a delayed menstrual cycle, as it is a critical condition that requires early detection and management.
Ectopic Pregnancy: In cases where pregnancy is suspected, an ectopic pregnancy is a life-threatening condition that must be ruled out promptly.
Ovarian Torsion: This is a rare but emergency condition that can cause severe abdominal pain and menstrual irregularities, including delayed cycles.

Premature Ovarian Failure (POF): Also known as premature ovarian insufficiency, this condition leads to the loss of function of the ovaries before age 40 and can cause irregular or ceased menstrual cycles.
Asherman's Syndrome: A rare condition characterized by the formation of adhesions or scar tissue in the uterus, which can lead to menstrual irregularities, including short-term delays.
Pituitary or Hypothalamic Tumors: Although rare, tumors affecting the pituitary gland or hypothalamus can disrupt hormonal balances necessary for regular menstrual cycles, leading to delays or irregularities.