Hey man, I have essentially the exact same thing. It started for me also, around the age 16, when I got my first hemmorrhoid and I also happened to be taking a course of Antibiotics at the time. The hemmorrhoid became a benign skin tag that just traverses my bottom now. I went to a gastroentrologist, and he said that the smell is coming from yeast from the rectum populating the skin externally, using the skin tag, or hemmorrhoid, as a bridge. One thing I've noticed though is that even sometimes when you don't seem to be sweating, the smell is still present.
The gastroentrologist referred me to a surgeon who wouldn't take the skin tag away as he said surgery could lead to further problems down the line, like leakage, so the solution then is not to tackle the hemmorrhoid but rather the odorous microbes. Try the anti-candida diet I'd recommend, I've tentatively noticed in the past month results but I haven't completely committed to it either.
Whatever happens, you ain't alone bruh