One question: do you have a behaviour therapist working with him? Biting is quite common. It's signifying something - quite probably anxiety (is he biting himself, or others?) Also, he may be hypersensitive to certain fabrics or materials, which is why he doesn't like the nappies. I work with autistic adults, and many of them have such issues. One of them refuses to wear any form of underwear.
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All the best,
Hi no I don’t I actually have no support for him apart me and family he got his diagnosis and that was it they left us to find out about everything on our own he’s biting others he never bites hisself I did think that with nappies as he doesn’t like clothes on at the minute