Autism "Regression" in Baby - or something more as well? 8 months

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I posted about eight weeks ago about our 'hard' baby. Lots of GI/silent reflux issues since birth. Tried all the elimination, hypoallergenic formulas, high dose PPIs etc. No change. Terrible sleep day and night. Baby very sensitive and dials up suddenly over seemingly nothing. Like walking on eggshells all day, extremely irritable. Wants to crawl and stand all day or be carried and walked around. Cannot sit still on lap. Changing clothes, nappy etc is very challenging.
We're running on fumes at 8 months.

By four months I knew we were having a very different experience to others, I put it all down to reflux/GI etc.

However, in the past 8-10 weeks I've noticed a shockingly marked decline in his eye contact, smiling, response to voice and general social skills. Laughs at objects rather than people. Hasn't reciprocal smiled for caregivers in weeks (but will for random strangers?)
I can already look back at videos from the summer and notice a marked difference in his eye contact with us.

He's had a 'motor explosion', learned to crawl, sit and stand but has regressed so much, with no sign of these nuanced social skills returning. No babbling yet, mainly raspberries and whining.

Hearing and eye sight seem totally fine. Still on PPI.
Have a paediatrician appointment this week (for reflux!) but want to discuss this. Have contacted GP and our equivalent of HV (not in UK) who said to speak to paediatrician first. Hoping for an OT referral (and the usual audiology etc).

Bizzarely, he does well with novel or new people and will often crack a smile for them.

Has anyone experienced this decline at such a young age? Could there be something more than ASD?

Afraid of the 'first time mum', 'watch and wait' response.

Mainly looking for someone who experienced similar/had similar concerns at this young age.

It's an extremely lonely place to be with no one to talk to/compare with.

We just want to do right by our baby.

Often when i see this type of post I think its a bit ridiculous and there is no way you can tell at that age but I would be concerned about the regression too.
Noone can tell you if it is asd or something else, my own asd child had signs when young but not that young. As you have said, speak to your health visitor equivalent, and I would bring it up with paeds.
Hope it's nothing x

I’m afraid you will get a watch and wait answer. I will say that although we didn’t go through regression I recognise a lot of what you describe otherwise. My Dd had physio at 18 months due to not walking, but she walked soon after.

she had severe food allergies and for a while I put all the hard baby years all down to that. But you mum instinct is there for a reason.

When she was 8 my DD was eventually diagnosed with AuDHD and dyspraxia. I would add that she has a great life and is loads of fun and is doing fine academically.

I would trust your instincts if you notice differences with other babies. I was constantly dismissed as a FTM.

I’ll be honest, my dd had signs of autism from birth, except we of course didn’t know, she was diagnosed at 2.5 which is pretty young, but looking back we had zero eye contact zero babbling, extremely discontent, late to sit, didn’t crawl they did walk at 10 months, very difficult with foods… so yes they can show signs BUT lots of other babies will exhibit these and not be autistic including my other dd.