As Remar mentioned, you can skip a period because of illness, stress, and things like extreme diet or exercise changes. However, there could be a hormonal issue or cysts that could be affecting this. You'll want to make an appointment with a doctor to rule those out.
Women can skip periods sometimes for no reason or, because of being sick, stressed or several other reasons. You may want to make an appointment with your Dr to find out what's going on.