Premenstrual syndrome, commonly known as PMS, comes with some uncomfortable complaints which are believed to be largely caused by the fluctuation of hormones and low serotonin levels that occur. There are more than 100 symptoms that have been noted as being related to PMS. 

Progesterone peaks during this time in your cycle and is followed by a sharp drop, and this is what causes PMS symptoms. These symptoms can range from non-existent to debilitating. To add insult to injury, at the same time your serotonin dips. The swift hormonal changes may cause symptoms, including:

• Headaches and/or migraines
• Weight gain
• Backache
• Mood swings
• Aggressive behavior
• Irritability
• Anger
• Concentration problems
• Increased appetite
• Anxiety
• Depression
• Water retention leading to bloating
• Cramps
• Painful or tender breasts
• Skin problems
• Constipation

When it's more than PMS

Up to 10% of women have symptoms much more severe than those experienced in PMS. These women have a condition called "late luteal phase dysphoric disorder," sometimes referred to as premenstrual dysphoric disorder (PMDD). For women with PMDD, symptoms are severe enough to be incapacitating and require medical attention.

Scientists have been unable to determine the exact cause of PMS or PMDD. Many researchers suspect that these conditions are caused by an imbalance of estrogen and progesterone, the hormones that influence your reproductive cycle. Other theories include hypoglycemia (low blood sugar), excess prostaglandin activity (prostaglandins cause abdominal cramping), changes in neurotransmitters (brain chemicals that can affect mood), and changes in opioid peptides (similar to neurotransmitters, they also can affect mood).