What Causes Persistent Nausea?

I am a 47 year old female. I have been having nausea daily for several weeks. I have a history of reflux and I am sensitve to many foods (especially dairy). I avoid dairy. I try to eat healthy and drink water. Six months ago I had abdominal pain (epigastric and lower) and my amylase was 108 (normal 100). I am currently taking antibiotics for endometritis, but I make sure I take them with food. I still have left lower abdominal pain a lot and feel nauseated every morning with no reflux. I had an episode of bright red blood on the tissue two days ago, but I think it s from a fissure that I have. I know I need a colonoscopy. I am also tired a lot and stressed. I don t want to blow these symptoms off. What should I do?