What Causes Nausea,vomiting,stomach Ache And Craving?

hello, I am a 16 year old girl. I typically go 5 weeks before having my period and it just ended last week. The weekend before i last had my period, I had sex but I am now experiencing extreme nausea, i am vomiting, weird stomach feeling, occasional stomach aches, cravings (which I NEVER get), and the feeling as if I am on or about to be on my period. (My period is very regular for I have been having it for almost 7yrs).