There are several reasons why a period may be delayed apart from pregnancy. Some of the most common reasons include:

1. Hormonal imbalances: Hormone imbalances and health conditions are the most common reasons periods are irregular or late. Hormonal imbalances can be caused by conditions such as polycystic ovary syndrome (PCOS) or an overactive or underactive thyroid.

2. Medications: Certain medications, including hormonal birth control, chemotherapy, and radiation therapy, can cause irregular bleeding and delay periods.

3. Stress: Stress can result in a hormonal imbalance and affect the hypothalamus, the part of the brain that helps regulate periods. Stress can also lead to weight loss or gain or other illnesses, all of which can affect the menstrual cycle.

4. Weight changes: Extreme weight loss or gain can cause hormonal imbalances and affect the menstrual cycle.

5. Health conditions: Certain health conditions such as diabetes, celiac disease, and chronic illnesses can affect the menstrual cycle.

6. Breastfeeding: Breastfeeding can cause hormonal changes that delay periods.

7. Uterine scarring: Menstrual cycles can also be disrupted or halted due to uterine scarring, which usually happens after a dilation and curettage (D and C) procedure.

8. Menopause: Menopause is a natural process that causes periods to stop.

Its important to note that the occasional odd cycle is nothing to be alarmed by, but if periods seem irregular or are delayed for more than 35 days, its best to consult a healthcare provider.