What Causes Abdominal Pain, Nausea With Vomiting And Acid Reflux?

female 26 nausea and sickness, i thought at first it may have been food poisoning however the nausea has lasted for 4 weeks now and i still vomit but not every day. it doesnt matter whether i eat of not (if i have not eaten i vomit shomach acid.) my doctor has done blood tests including a pregnancy test which was negative. it did show i am anemic but didnt highlight anything else. other symptons i have is fatigue, centre lower abdominal pain (below my belly button), dizziness and lower backache. no missed period. can you help?