What Causes Diarrhea, Nausea And Back Pain?

I have been feeling unwell for the last couple of months - symptoms are diarrhea, nausea, pain down left hand side, sore back across kidneys, have low blood iron results, dizziness, aching arms and legs, swollen feet, stomach pain, headaches, very very tired, especially at nights, arms and legs feel so heavy. All blood tests come back ok but low in iron iron, faeces clear, urine clear.