What Could Sudden Delay In Periods With Headache And Sickness Suggest?

Hi, I'm 14 and have been having my period for 2 years. I've never had and irregular one. I had sex recently but nothing happend, he didn't ejaculate. But I've been feeling really sickand stressed out, I think I've got a bit of flu, the symptoms I'm suffering from are I feel really weak, I have a headache every morning and feel a little bit sick. Also I just finished my period like 5 days ago and I started again yesterday. What is wrong with me?!?! I'm really worried!