Aggressive outbursts with autistic son

Just lately my son has started having unpredictable and aggressive outbursts with myself and his siblings. There is no real trigger for when it happens it just seems to happen. He can go from playing to shouting, screaming, hitting and crying all in the matter of seconds to minutes. He only got his diagnosis this year, but due to his consult discharging him after this diagnosis i’ve had no further support for him. I contacted his GP today, who is going to get back in contact with said consultant. 

i’ve tried talking to my son to find the cause of these outbursts but i either get a stare, no answer, animal noises, or he doesnt know/doesnt remember. He has his own safe space in his room which we encourage him to use especially when hes upset/distressed. But because he shares his room with his step brother this can still be a challenging time for him.

is there anyone else who has had this kind of experience and what have you done that you found has helped?