Think you're the only one who experiences sudden food cravings, crazy mood swings, or cries at the drop of a hat during your period? You're not alone, explains Dr. Lisa Sanders, New York Times columnist and author of Every Patient Tells a Story. "The suffering is universal," she says. "Eighty percent of women get the occasional PMS kind of symptom - a little bloating or irritableness - but then 30 percent of women have this [feeling] regularly, predictably, and can tell their period is coming because they feel so darn bad."

Dr. Sanders lists the key days of your period and the changes your body experiences:

Day 1: "This is how we count the cycle, starting with the first day of your period."

Day 5: "You still feel pretty good - your hormones are at low levels, and then they slowly begin to rise."

Day 14: "Estrogen reaches its peak. Progesterone is also rising and you still feel pretty good."

Day 16: "Both your estrogen and progesterone drop dramatically. And it's this dramatic change that triggers a lot of the symptoms that make you feel bad. On Day 16, the women who are most affected will start to feel bad."

Day 22: "Progesterone is starting to rise again, and most women who are going to have PMS start to feel a little something."

Day 27: "People who have PMS feel a lot because their hormones drop like a stone again."

Dr. Sanders adds that if you experience any of the following symptoms in the week or so before your period starts and if they go away after your period starts, you might have PMS:

• Bloating & fatigue. "Ninety percent of women complain about these two symptoms. In addition to abdominal bloating, there are women who have really significant fatigue in the week before their period."

• Breast tenderness. "The breasts are sometimes larger but certainly more tender."

• Moodiness & irritability. "You'll be fine one minute, crying the next minute and laughing the next, and nobody knows what to expect from you. People complain - things that shouldn't bother them do."

• Sugar cravings. Fifty percent of women complain of either craving sugar of having some change in their appetite, usually having a bigger appetite.

• Acne. "When your skin looks like you're 15 but you're really 35, you might have PMS."

Watch the video above to see Dr. Sanders explain how your brain is affected during your period, and for her recommendations for getting through this difficult time of the month.