You should get a home pregnancy test (hpt) done if you're worried that you're pregnant.. You can get that device from ur local pharmacy.. It's an accurate and inexpensive test.

Other than that..... I would say that it's normal for a girl who's 14 to miss periods, cuz your cycle isn't very stable yet. It takes about 3-4 years before your period will stay on track. Every girl has her own internal clock. If you're constantly stressed out, you could miss your period as well. As well as losing a lot of weight in a short period of time. But, do the hpt and see what it saids. If you are still unsure.. Go see a doc and have a blood test done to find out for sure whether ur pregnant or not.

Good luck and hope I helped you. =d