Welcome, although I'm sorry you have need to be here

Everything you wrote sounds VERY familiar to me (and I'm sure to many of us). In terms of your son's physical development, I wouldn't worry. My daughter was late at everything, and while it was annoying for us at the time, she eventually did everything and was fine.
We noticed a big change in Sammy the very day he started crawling. It was like he was finally able to get where he wanted to go, and his fussiness decreased substantially. When he started walking, we noticed more improvement. When he started talking, more improvement still.
I definitely relate to feeling like your son is never happy. I used to look at Sammy and think, 'you have everything you need, WHY can't you just be content??'. My personal, totally non-scientific opinion on this is that high need or 'spirited' babies/toddlers are hyper-sensitive to everything...the slightest discomfort (hunger, thirst, wet diaper), to boredom (play for 2 minutes, and then start whining), to separation anxiety (you can't even *think* about leaving the room to go to the bathroom without them crying). At least for my son, when we were doing things that were super-intense, like bouncing or swinging him (BIG bounces, and BIG swinging), were around LOUD droning noises, in crowds, or basically doing anything that a normal person would find totally assaulting to the senses, that's what calmed Sammy. It's like they need that intense stimulation from the outside to distract them from the discomfort they feel on the inside.