Sorry you continue to be in pain and have so many different problems.
The hemorrhoid sound like a sentinel pile, which is what happens when a fissure goes from the acute stage (before about two months) to chronic.
Are you seeing a colon and rectal surgeon(CRS)? You have mentioned going to the doctor a few times, but if you are seeing a GP they know basically nothing about fissures, and the longer you wait to see an expert the worse a fissure can become, creating scar tissue etc.
The doctor saying that the hemorrhoid can be the cause of the mucous I have not heard of before, but irritation of the fissure can certainly give you bloody stools and mucous.
Your best bet, IMO, is to have an examination, possibly under anesthetic, by a CRS who can tell you what is going on so that you don't have to guess at it, and continue suffering.
Sorry for your pain with it all. Can definitely empathize there!
Sav