What Causes A Delayed Period, Tiredness, Stomach Sickness, Moodiness And Vaginal Discharges?

Hi, my name is Tiffany and I'm 19 years old. I haven't had my period since the 17th of may and I am usually on by now, but I'm not. I have been very tired, sick to my stomach, moody, eating more than normal, gained a little weight, and just this morning had some light brown discharge. Could you tell me what is going on?