Why Do I Puke Blood ? I Have Abdominal Pains, Digesting Problem .

Hi, I am a 23 year old, white female. Quick history. I occasionally have minor issues with digesting complex foods, milk, etc...Stomach pains ( upset stomach ) are quite normal for me after a meal . I take birth control (Sprintec) and an antidepressant (Citalopram 20 mg) on a daily basis. I am currently experiencing abdominal pains, mostly on my lower left side near my descending colon(?), occasionally it migrates to above my uterus and also on the right side. I am also quite bloated. These are not menstrual cramps. I am very weak and nauseous majority of the time. I have expelled blood with my bowel movements last on Thursday and Friday of last week. I went to the emergency room last Friday when the pain on my left side became unbearable. As usual, the doctors couldn t have cared any less with regards to finding a reasonable explanation to my pain(s). My blood and urine tests came back clean, as did the CT scan of my abdomen/pelvic area. They gave me some painkillers, antibiotics, anti-nausea medicine. (Dicylcomine, Hydroco, Promethazine, and Ciprofloxacn) The newest thing is that I am burping/puking blood or bile?? The color is a dark brown and a little chunky. This did also occur when I was about to leave the ER. Thank you in advance for any insight or direction to my problems!