You should have a complete digestive stool analysis (CDSA) done. This will show up dysbiosis/yeast overgrowth.
I have read that constipation that is not relieved by diet/lifestyle changes is generally due to an imbalance of gut flora...lack of good stuff and too much of the bad stuff.
Im in Australia but I know genova diagnostics and doctors data do the CDSA. Also get the functional liver detox profile (FLDP) done as the gut would put a toxic load on the liver.