I've read that a blockage in the intestines can cause fecal body odour and I think constipation could easily cause a blockage, even if partital blockage so you can still poo. I'm too struggling with fecal Body Odor and I noticed I can smell my odor at certain times through my chest so I believe air expelled through my lungs, maybe try and see if you can pickup a slight smell anywhere and the guys on the forum can hopefully help better, best of luck hope you get cured dude! :)