29 yr old female with gerd. now has loose, infrequent (2-3 days) yellowish brown colour stool with incomplete evacuation bloat, gas, odor. any causes?

Many possibilities: This is unlikely to have anything to do with your gerd unless you are being treated for helicobacter pylori with antibiotics (which may touch off things like cl. Diff colitis). This may be viral, or giardia (an amoeba), or bacterial, or rarely may signal onset of inflammatory bowel disease. If it does not get better quickly (24-48 hrs) please see a doctor for diagnosis and treatment.