What Is The Reason For Delay In Getting Period?

Okay So I am 14 and I got my first period in March 2 days before my 14th birthday and i was supposed to get my period 2 days ago and i didnt get it. I have never had sex let alone kissed a guy and I am very stressed about this and I have no one to talk to about this so please help. And I have 2 resons to be stressed I start high school in less then a month and I have gained 2 pounds in the last week I dont know why but yeah sorry for rambling but if someone could please answer my question that would be great.