What Causes Delayed Periods And Lower Abdominal Pain?

I am a female, 18 years old. My height is 5ft6. I have had no past medical problems. I am 2 weeks late for my period , I am experiencing severe pain in my lower abdominal for the past week. I feel bloated and frequently urinating. I feel sick after I eat but I don't throw up. I had unprotected sex 3 weeks ago , 2 weeks ago and last week. What is this ?