Hi, and thanks for your medical question on eHealth forum!
Some amount of mucus is always present in stool. Mucus can be due to internal hemorrhoid or it can also be due to amoebiasis (if you feel an urge to pass stool) which is an infection. It is effectively treated with metronidazole and tinidazole. You should get your stool examined for this infection. At times a hemorrhoid is associated with fissure and this too can be a cause. Inflammatory bowel conditions such as IBS, Crohnâs and ulcerative colitis too can cause mucus in stool. These can be diagnosed by colonoscopy as well as endoscopy (this you had).
If you have irritation and mucus in mouth, it could be due to giving up tobacco chewing. However, it can also be due to acid reflux despite a normal endoscopy. I suggest you take a second opinion from a gastroenterologist and start omeprazole for this. Also, consult the GI doctor regarding the other possibilities. Hope this helps. Take care!