What Causes Persistent Stomach Pain,nausea And Back Pain Despite Suffering From Gastritis?

I have gastritis. I ve done lab work which all returned normal, including testing to rule out pancreatitis. I ve had an ultrasound study of my gallbladder and kidneys. It was normal. I improved some while on antibiotics, pepcid and a ppi. I m not only on the ppi. I haven t gotten much better, having a stomach ache all the time. I often feel nauseated and starving at the same time and my stomach growls loudly. I also have pain in my lower back near my right kidney. My cultures have come back clear so I seem not to have kid eu infection. I feel terrible after I eat. It seems to get much worse when I have my period. Is there any reasonable explanation for that? Do these symptoms seem consistent with ulcer? I have an endoscopy scheduled in a couple of weeks.