What Causes Delay In Periods, Constant Vomiting Sensation And Breathlessness?

Hi im 21 years old and have been feeling really bad lately. First of all i just thought it was stress with uni deadlines but its getting worse. I havent had a period for two months ( definately not pregent as not had relations and have been tested anyway). I have a constant sick feeling deep in my stomach and even a trip to uni leaves me out of breathe and desperate to sit down. I have only been sick once but cant get rid of the sick feeling. Do u have any ideas