ive been feeling very nauseaus, my breast are tender, i have headaches and back pain, i feel the need to pee really bad but i only go a little bit, everytime i smoke a cigarette i feel sick, my emotions have changed, fatigued, i also get period like cramps but it leads to diaherra or constipation. I have not missed my period yet but i have taken a pregnancy test that came back negative. Can i be pregnant?