What Causes Metallic Smelling Stools With Constant Bloating?

I am experiencing metallic smelling stools, constant bloating, sometimes painful transverse colon on palpation, passed some blood about a year ago, but none detected in stool test, iron deficiency anaemia, fatigue concurrent with episodic diarrhoea. Seems to be independent of diet. Probiotics and progesterone have helped to tone down the diarrhoea, but metallic smell remains, especially after a soft stool. Any ideas? I was thinking ulcerative colitis, and I also get ulcers in the mouth, but I'm scared to get a colonoscopy.