Light brown/yellowish stool for week or so, indigestion, pain in lower stomach, nausea, pain in sides, have acid reflux, been taking tums (calcium carbonate) frequently, some pain in upper & lower back, pain in neck.

Need to be examined: Sounds like you have several problems and I doubt they are all related. I could give you a list of all the possible causes of any of your complaints but it won't be helpful. A physician would listen to your complaints, take a history of past medical problems and ask you numerous pointed questions to point towards a diagnosis. He would then examen you. All of which we cannot do here on HT.