Polycystic ovarian syndrome (PCOS) is a very common endocrine disorder often associated with symptoms such as irregular menstrual cycles, weight gain, hair loss, acne, hair growth in places women don't want (upper lip, belly, etc.), and infertility. It can often take a long time to diagnose because some associated symptoms are often chalked up to 'typical' of girls in their teenage years such as acne or irregular cycles.
Pre-menstrual syndrome (PMS) is that time of the month just before a woman’s cycle starts where her hormones may feel completely out of balance resulting in mood swings (!), tender breasts, weight gain, acne, and fatigue. The hormones responsible are primarily a balance between progesterone and estrogen however other hormones such as cortisol (from the adrenals) and serotonin (the brain hormone) can play a role.