My DS didn’t speak a word until he was a little over 3. His understanding was great, he’d mimic phrases back in the same tone of voice I’d used eg I love you, he’d ‘say’ back I love you too, but it was nasally noise. He too would hit himself repeatedly. It was utterly heartbreaking, because he was trying so hard and just couldn’t do it! Didn’t help that he’s a twin and his sister talked easily, and his 27m check was during lockdown 1.0.
His speech did eventually happen, his first word was mama and it was the most beautiful moment, I cried! Ultimately, I’m still fighting to get him help, (he’s 6 now) and nobody has been able to diagnose a reason for it. He talks non stop and his speech is much better, vocabulary is great, but you still need to be tuned in to him to understand every word especially when he’s having a language explosion.
Is your son in nursery? That helped mine, in a weird way it’s like he had to figure out how to make himself understood better. They were superb with him, and came up with multiple strategies to help him cope. We saw a private ent who referred him for a hearing test (all good) and have been stuck in an infuriating loop of NHS ent/salt/hearing tests (he’s had 4 so far)/generally being fobbed off for years until the last 6 months or so and have finally managed to get speech therapy approved at school after being rejected by them previously for help.
It’s been a long road, but I think we’re getting there!
Things that might help:
Hug him when he hits himself, and explain the emotions he might be feeling and explain that you understand,
Keep talking, trying to get him to say the words himself. Try not to make it too easy for him to get what he’s after without trying the word himself (I hated this, seemed cruel to pick on a kid who was already struggling with speech!),
Praise, lots and lots of praise and encouragement,
Keep pushing for help,
and, keep a diary of when he hits himself, and what the circumstances were leading up to it to avoid a 6m wait for the next appointment!