Irritability, anxiety, sadness, bloating, headaches, brain fog, food cravings, acne, and more…why do I experience PMS each month and how can I avoid it? PMS is mostly caused by fluctuating hormone levels estrogen and progesterone. Estrogen is our main reproductive hormone. It boosts serotonin levels, gives us energy, builds muscles, and improves insulin sensitivity - it’s the hormone that peaks right before ovulation, and that’s when it should be at its highest. But, too much estrogen during the luteal phase can be overstimulating which results in breast pain, fluid retention, irritability, and headaches, i.e. all the period symptoms we don’t want.