Appetite Loss, Breathing Difficulty, Feeling Of Fullness, Vomiting Sensation. Pregnancy Test Done. Reason?

Hello, I have some questions to ask you because i don t know what to do and i need advice from you as a doctor..So my problem is this: Before 7 days I came back from my holiday which I spent with my boyfriend and I started to feel some things that I never felt before..I m 17 years old and I have problem with the eating..Every single day in these 7 days when i take something to eat- I can t. I normally eat 3 to 4 times in a day but now i can t even 2 times..Up there under my breast in my stomach i feel something like to have a strong belt under my breast and in some moments I can t take breath so i need to take deep..When I take to eat I eat just little little bit not even a half slice of a bread cos I can t eat more..I feel full and after 2-3hours i start to feel that I m hungry but again i take something to eat and i can t i feel full..In some moments I also feel that I m going to throw up and that s usually after eating or when i sit on the computer but I never did it.. I was scared that I m pregnant because we had unprotected sex with my boyfriend but he never finished inside my vagina so I can t be pregnant and I did test to be sure for it and it was negative..My period should start after 2 weeks..But the problem is my stomach, I can t eat normally as always.. What advises you would give me and can you help me in some ways? Thank you and your reply means lot to me