What's wrong with me?! Dizziness, fainting upon standing, & more...?

Okay, so I spent some time in the hospital last week. I was getting very pale, felt dizzy and like fainting upon standing, was having black, tarry stools. I had an upper endoscopy done (while AWAKE mind you) and they did blood work. They told me I had no BLEEDING ulcers, that my gas-reflux was harming my esophagus though, and that my hemoglobin was 7.4 when it should be 12. So they put me on Protonix and Zofran, I must take Iron and stay away from anything with Aspirin/Ibuprofen/Naproxe... and try to cut out a lot of caffeine and gave me two units of blood. I felt better. But since getting out I have started to get a little dizzy again and my diarrhea is black and tarry just like it was. I don't get it. I don't put ANY pills in my mouth aside from the ones they told me to take. I cut out a lot of caffeine. I'm 25/female/had a gastric byp & gall bladder removal in 2003. Help! If I left anything out, ask please.