3 y/o with possible autism and potentially other issues

My boy turned 3 years old in August. He's a very happy little chap the vast majority of the time. We noticed that he's incredibly intelligent from a young age but he's fallen far behind with a lot of milestones. His mother and I thought it'd all sort itself out once he started talking but he still hasn't said a word.

He knows his numbers 1 - 25 and will find each one when asked. He knows sooo many animals and has great interest in them. He can identify brown bears, black bears, polar bears and can pick out a Gecko from a Skink and can pick out an Iguana from any common lizard. I've also been doing insects with him and, most recently, we've started exploring space and all of the planets in our solar system. He picks everything up so quickly.

However, he just looks at us blankly when we ask him to wave. He can shake his head for "no" but won't nod for "yes". We're in the midst of potty training but his lack of speech has been a real challenge as he can't tell us when he needs to go for number 1 or 2.

He also doesn't show any real interest in interacting with other kids at nursery. The nursery staff are great with him but have flagged some things to us and have suggested he see a doctor and get a referral to a pediatrician (we're in England so it works differently to the US I think).

He saw the doctor today. My other half said the doctor was concerned that we hadn't approached them with this yet as he's "very far behind". He is our first child so as far as we are concerned he's just a normal kid who's just a bit behind but will catch up as soon as he starts talking. I dunno... I get the impression they're possibly seeing more than just minor autistic traits and it could be deeper.

I'm trying to reassure my other half by saying none of this is a problem and that we just need to get him whatever help he needs and that he'll be absolutely fine but I just can't help but speculate on the future. All the "what ifs" and such. How will he get on in a school environment? Will he get bullied for being different? The possibility of Autism doesn't bother me. It's just not knowing and the thought of him having a hard time in life.

It's just getting to me I think but I'm just doing my utmost to wear a mask to show my other half that there is nothing to be worried about. I know she's taking it all pretty hard and she's already asking me questions like "what have I done wrong?" to which my response is "absolutely nothing, some things just happen and are completely out of our control".

Apologies for the emotional dump of feelings.

For Dads that have been in this stage of limbo whilst you're waiting for appointments to get your child assessed, how have you handled it and can you please offer any advice or your own stories?

Many thanks