Hi @Nifty123 ,
I am so sorry that your son is not improving.I would call your CAT Team that should follow up after a visit to the hospital. It might be called something different in other states, check this link here for relevant numbers:
https://www.healthdirect.gov.au/crisis-management
I'm surprised your hospital has not informed you of this. If he is talking about self-harm with friends, he definitely needs support from his mental health team. I would also remove anything in the house that could potentially lead to self-harming (My friends had these problems with their son, so they used to remove sharp things, medications, etc... They would also take turns to make sure he's not unattended).
I hope this helps and remember to take care of yourself too :). Hang in there, we're here to help and let us know how your son is doing.