Vomiting dark green-blackish bile, back pain, but no fever?

I've been vomiting since around 7:30 last night, and the nausea started around 2. I figured I was just nauseous and I didn't think anything of it. So I went to work at 5:30 pm and started becoming extremely nauseous, so bad that I couldn't talk to customers so I told my manager and she let me go home. The instant I got home, I started vomiting. The first time it was food, the second time it was dry-heaving, the third-fifth time it was dry-heaving, mucus, and yellow bile, and the sixth and seventh time (which were while my fiance and I were in bed), I vomited dark green bile (almost looked black). He keeps saying it's the stomach flu, but I have no fever. Although, I do have a lot of pain in my lower and middle back. I didn't know if that was from bending over and vomiting last night, though. Please help me, I can't find anything that fits the symptoms. Thank you!