Missed period can be caused by other change in your body apart from pregnancy. Some of these changes include excessive weight gain or loss, increase in exercises, illness, emotional stress, hormonal problems, some birth control methods, a lot of travelling and many others. However, it is important to see a gynecologist so as to find out.
I am in my 20s and have had that happen before. more than likely next month you'll get it twice. thats what happened to me. If you have been stressed really badly it can effect you like that as well. periods can be crazy things.