Severe anxiety in 5 year old - wondering about medication

Hi all, I have a nearly 6 year old son who was diagnosed with ASD a year ago, although it was suspected before that. His speech was very delayed as was his social skills.

He’s always been quite an anxious child, but he’s always been able to enjoy himself - until this summer. He will have what seems panic attacks when we go out and arrive somewhere (he’ll be fine and happy to actually go before that), and his reason is usually ‘it’ll be late’ (It could be morning, he’ll still say it’s going to be late). He always becomes upset if his grandmother stays ‘too long’ (although what exactly is too long changes all the time) and it’s like a switch flicks in his head and he gets very upset and panicked until she leaves. He gets very distressed if someone on TV is the ‘same’ as in real life - e.g if he’s eating and there’s food on tv, if someone has no shoes on and he also has no shoes on.

It’s very upsetting for us to see because it’s such a big change in him - he used to enjoy soft plays and going to the beach, but even if we do somehow manage to get him out of the car he will, unpredictably, start panicking and scream to come back. We’ve tried to identify any sensory stimuli that could be triggering these but there isn’t any from what we can tell.

He’s doing well in school with a 1 to 1 worker, but whenever we arrive he will get a panicked look in his face and tell us he’s scared - despite the fact he doesn’t seem to know what he’s scared about. Once he’s in school he’ll be absolutely great all day, but constantly want to know the time. He also has a 2 year old brother who is very confused as to why his brother doesn’t want to go to parks with him etc to play anymore and he of course doesn’t understand :(

We've spoken to a psychologist and got some tips such as making sure he is 100% aware of what will be happening in his day and when he'll be home but unfortunately its not helping.

I am wondering whether medication could help - I'm aware that SSRI's can help anxiety in children. I feel a bit…wrong in asking about this to his psychologist though, almost as if we’re trying to stop him being ‘him’ - but right now he’s just not the happy boy he should be and just seems to live his life with constant anxiety :( does anyone have any advice?

Thanks!