I've experienced this - in my case caused by dirofilaria infestation (you get bitten by an infected mosquito), they completely physically block the colon, until you start clearing them, you'll be constipated and nothing works, even enemas worked just a little bit for me until I started clearing these
not sure if you have this, just mentioning it so you are aware that some parasites cause a physical blockage (when they are alive) and nothing but clearing them helps, at least that's based on my own experience