I had something similar. Chronic constipation and smelling like poop specially in the armpits. I have had similar comments too. My constipation was so bad that sometimes I used to get blood in poop.
I was contemplating of going to doctor for years and then finally i went to gastroenterologist for my constipation. He did colonoscopy and told me usual stuff like eat fiber, drink water, etc. He also said lots of his patients get problems from dairy, so I should look into that.
Long story short, what worked for me was quitting milk.
I used to drink two glasses everyday. I used to drink everyday since I was underweight and didn't want to cut down on any calories. After I stopped milk, my BMs got regular(every morning), they got smooth, they don't come out dry anymore, no burning, no blood.
My back Acne cleared up, appetite went up, gained some weight, but most importantly the poop smell is gone. I could sniff my armpits for any hint of poop smell and there is none.
What i noticed is even my farts don't smell as bad anymore. Sometimes they don't smell at all.
So i would say you should try to resolve constipation and see if that helps.