Really struggling with 2yo tantrums and behaviour

[Jemimapuddleduk]

I am really struggling with the behaviour of my 2 yo ds. So as not to drip feed and to give a bit of background he has had a very rough ride with lots of illness in his first year then diagnosed with AML at 16 months and spent the first 6 months of this year in hospital undergoing intense chemo. I know we are so, so lucky to have him here and that he is currently in remission.
He has always been behind developmentally (at 9 month check before cancer diagnosis). At his 2 year check he wasn't scoring on the 24 month or 12 month assessments still so we have a referral to the community paediatrician in January. He doesn't speak at all yet but can babble quite tunefully. Mornings are usually ok as we get out to activities and he does enjoy these but doesn't interact with the other children and is happier left to his own devices just roaming around. Afternoons are very challenging. He tends to nap from 1-3 then wakes up in a foul mood and just cries and tantrums constantly. He has spent the last 90 minutes laid on the floor crying and if I try and distract him with a toy he will hit out at me. I am finding it really hard and exhausting. If I take him outside (which I haven't done today as it's chucking it down) he is very happy but will only walk where he wants and will lie on the floor if we go in the wrong direction or when we head back to go home. Again he will hit and scratch if I try to pick him up. I suspect a lot of this is frustration at not being able to speak.
I suppose this is a rant more than anything but any words of wisdom, support or advise much appreciated.