I feel your pain. My old blind/deaf Queensland heeler (a rescue) had severe intestinal issues - we think he had some kind of cancer - and while he was completely housebroken for 10 years before I adopted him, he quickly degenerated as he got sicker and sicker after I brought him home. He had one severe gastrointestinal infection and never recovered.
Soon he could not hold his bowels at
all and was having bloody diarrhea all over my house on a daily basis, even though I had him on antibiotics and anti-diarrheal medication. Imagine coming home from a long day at work and having to scrub blood and liquid poop out of a brand new white carpet (I have obsessive-compulsive disorder too, so needless to say, I almost had a nervous breakdown during this period...)
I ended up putting him down in September after owning him for only four months because I was so overwhelmed by his illness and he had already cost me at least $150 in vet bills for every month I had him...
Now my new yorkie pup Ollie is having minor housebreaking issues, but it's a BREEZE compared to the problems I had with my sick old dog; the size difference in poop alone is staggering to me.
Good luck with Nikko, he's a doll baby!