GERD and anemia question

I was diagnosed with GERD about five years ago. My symptoms are atypical: there is a kind of quiet "burp" that my esophagus does, especially after I eat something (it's not a normal, hearty belch), but I almost never have felt the sensation of heartburn. My doctor has urged me to take 20.6 mg omeprazole (Prilosec OTC) daily. It doesn't seem to make any difference, but I do it anyway.

Here is the question: At my last physical, I was found to be slightly anemic. My physician suspects that GERD is causing a tiny loss of blood in my esophagus or stomach and ordered an endoscopy. But which is more likely: that the anemia is caused by poorly controlled GERD, or that it is caused by the Prilosec I am taking to control GERD? I have heard PPI's can interfere with the absorption of minerals.