What would be the reason for your breasts to start hurting 4 days after period and last 16 days?

There are many potential causes for breast pain that lasts for 16 days and begins four days after your period. It's important to see a healthcare provider for an accurate diagnosis and treatment plan. Some possible causes include:

1. Cyclic breast pain (Cyclical mastalgia): This is a common cause of breast pain that is related to the menstrual cycle. It typically occurs in both breasts and can range from mild to severe. It's thought to be caused by hormonal changes during the menstrual cycle.

2. Ovulation: Some women experience breast pain around the time of ovulation, which occurs about 14 days before the start of their period. This pain is usually mild and resolves within a few days.

3. Pregnancy: Breast pain is a common early sign of pregnancy. It can be accompanied by other symptoms such as nausea, fatigue, and mood changes.

4. Breast cysts: These are fluid-filled sacs that can develop in the breasts. They're usually benign (non-cancerous) and don't cause any symptoms. However, sometimes they can cause pain, especially if they're large or multiple.

5. Fibrocystic changes: These are non-cancerous changes in the breast tissue that can cause pain, tenderness, and swelling. Fibrocystic changes are common in women of all ages, but they're most common in women in their 30s and 40s.

6. Mastitis: This is an infection of the breast tissue that can cause pain, swelling, redness, and fever. Mastitis is most common in breastfeeding women, but it can also occur in non-breastfeeding women.

7. Breast cancer: In some cases, breast pain can be a sign of breast cancer. However, it's important to remember that breast pain is a common symptom of many benign (non-cancerous) conditions. If you're experiencing breast pain that's persistent, severe, or new, it's important to see a healthcare provider right away.

Your healthcare provider can perform a physical exam, review your medical history, and order diagnostic tests such as mammograms or ultrasounds to determine the cause of your breast pain and recommend the appropriate treatment.