what does it mean when you receive your period for sometime¸then one month later don't get it?

Hi, Anon. Welcome to Empowher!

Women's cycles can be very irregular, especially when they are young. It's not uncommon to be a couple of weeks late -- or even skip a month -- and then get right back to normal.

Menstrual cycles and periods are a function of the hormones in your girlfriend's body. As her estrogen and progesterone and other substances rise and fall, her cycle takes place. If those hormones are out of balance or are changing, her cycle can be irregular.

Is your girlfriend very thin? Sometimes when a woman diets too much and becomes too thin -- for instance, with an eating disorder -- her period will stop. Similarly with the exercise that you mentioned, though it sounds like that's not an issue right now.

I'm interested, you say you want your girlfriend to be safe and protected; may I ask what from? What are you most worried about? Of course a common cause of a missed period is pregnancy, but since she is a virgin that would not be the case. Or have you experimented enough with sex that you are concerned about this?