Help, I can't help feeling something isn't quite right with my 4 year old step son

I have had concerns about my 4 year old step son for sometime but haven't really been able to put my finger on what is wrong, he slept very poorly as a baby, was awake for a day after he was born and seemed to need to be settled constantly or cuddled. He would wake up frequently until he was about 2 1/2 and still now wakes up in the night most times we have him. He was very delayed in starting to talk, and did no babbling when he was younger. He is very easily distracted and needs to be given instructions several times before he understands.

He is more often than not a nightmare to get food into, gets distracted and sometimes just seems to have no interest in eating at all. He is well below average for height and weight but seems to be following a line with this.

He seems very unaware of things that go on around him, we ask him questions about things he has done and he doesn't seem to understand or know what we are talking about, he has recently got a pet rabbit at home and hasn't talked about it at all to us, not even to tell us it's name.

I have 2 daughters myself, one a year older than him and one 2 years younger and both are so different to the way he is, the younger one sometimes seems to be more aware of her surroundings than him.

He can be extremely hyper, running around squawking in a high pitched voice and then be completely lethargic and tired only a few hours after waking up. His moods can be very unpredictable too going from happy to very stroppy quickly and sometimes for no reason. He can be very rough and likes to bash things constantly and often breaks toys and other items.

His balance isn't great and he can sometimes be extremely clumsy, walking into things or falling over and has often fallen and forgotten to put his arms out to stop himself.

He also constantly has things in his mouth, chewing and sucking toys, his fingers and all sorts. And when he is being told off his fingers go straight to his mouth or he pulls his face around and won't give eye contact.

Does anyone who has had a diagnosis think this sounds familiar to any of their stories?

Having read about SPD I feel there is a lot that fits with him but it's hard to know.