ADHD

Too early to say anything to be honest. A lot of it are normal toddler boys traits too

My eldest has ADHD, they won't test until 6 at the earliest I think. My 3 year old is exactly the same and it's got worse since I've had my 4 month old for sure. More likely just adjusting to a new baby tbh. All the doctors will say at this age though is keep a diary and speak to any nurseries as theyre all common traits for that age group x

His behaviour change in the last 2-3 weeks is potentially him not knowing how to manage his emotions of the new baby

I have had similar concerns with my daughter. I find it's hard to get across how challenging it can be and I'm often questioning what's normal 3yr old behaviour and what isn't.
I think trust your instinct, but there's not a lot that can be done right now. I have approached the health visitor for some specific concerns like sleep so that it's on record. And then I'm keeping notes of behaviour that I feel may be linked.
Also just trying to learn as much as I can about neurodivergence to try and help her manage her emotions etc. Even if it turns out she's not ADHD this is helpful!

But it's exhausting 😅 we'll often have days where she's awake 5am - 9pm and she does.not.stop. 😴😂

His behaviour with a new baby will change speak with health visitor. We on the systems for my sone who nearly 4 for autism (strong family history) who melt down understanding of feeling other his learning we've only just mange to toilet train tho when goes school he still ad accidents not eat at school when he eats at home it's same food and way he pushes everything I'm at once night mare. But speak to health Vistor get concerns dwn keep notes as they don't diagnosis it until their nearly 7