Chronic constipation getting exponentially worse.

Hello, so I (20M) have been dealing with chronic constipation for about 3 months now, this initially started as lower back pain 7 months ago, but with me being off of work has steadily gone away. The constipation was initially solved with stimulant laxatives, those then stopped working, I then used suppositories which briefly worked. I then did some research and most of my symptoms I concluded linked up with Neurogenic Bowel Disorder, so I attempted digital stimulation, which worked 3 or 4 times but then stopped working. My doctor prescribed me Linzess, and I take it with a generic version of Miralax, this has proven the most helpful, though recently it’s been doing nothing. This constipation is getting progressively worse, and when I do have a bowel movement it’s this sort of brown water? Not a watery diarrhea, not solid at all, it is just a brown water. I also consistently have this heartburn feeling in my lower abdomen, I’d say for 4 or 5 hours at a time, and it’s not painful but it’s extremely unpleasant. This is extremely concerning for me and my doctors don’t seem to be taking me seriously, I’m half considering going to the ER because I’m just running out of options. If anyone has any opinions whatsoever please shoot them my way.