EXTREMELY WORRIED

hello girls so heres the thing i had sex may 13th and have had my periods since then every single month but i wake up extremely nauseous and have very weird sypmtoms  do you guys still think i could ne pregnant? What should i do im 18 and completely stressed i can barely even sleep from how worried i am i even cry at night from how worried i am.  Took a test and came back negative 
God bless thanks for the support