I was this kid all throughout my school years.
Parents never taught me any kind of personal hygiene, and my house was filled with a thick smog of smoke, so my sense of smell is still shot to this day. To give an idea how bad it was, I was asking for dentures when I was 14 because my teeth were literally falling out. The water in our house was spotty at best, on top of the hygiene thing, so baths were maybe once every 2 weeks or so. My parents always had a fridge stocked with Coca Cola, but almost never drinkable water.
Besides pointing at my parents, I don't really have an explanation for you, but I've definitely "been there."
It took a lot of effort, but I've come a looooong way since then. Like... unrecognizably so, thankfully - other than the dentures, at least.
If anyone is reading this, and in a situation where their home life or depression or whathaveyou is putting you in this kind of situation: Just know that things can and will get better. I know how difficult and embarrassing it can be when you're deep in it, but all you gotta do is be a little bit better than yesterday (when you're able). It takes time, but it's totally worth it.