Awwww, sounds like how my son used to be. it was heartbreaking. they want to be held but they cannot tolerate it. It is worse too after having to be changed like that ( I know it had to be done). That just increases the meltdown because of not wanting or liking to be touched. I could never soothe my son either, he would just sit on my lap and cry he would try and hug me but just couldn't. I am sorry. I will tell you there is light at the end of the tunnel. Also, my son used to wake up in the night as well, but screaming like night terrors. It was usually when he had an over stim day. What I can tell you is this...
Once his therapy kicked in, the brushing technique, weighted blanket, deep pressure, sensory activities, it all worked!!! He still has to be asked to be touched, I think I am the only one that can touch him and hug him without having to ask, all others have to ask. the worse thing is restraint, first because they do not like to be touched like that. I know he is young, we need to help you find a way to persuade him to be ok with a task. Something ot hold that is specifically for changing time, maybe something heavy. If it is during the day and you can see a meltdown is going to happen jump into action! Once they are in the meltdown there is not much that can be done, you have to wait it out. they have shut down because everything has become too much. Never think of him as being a behavior problem or defiant, he cannot help what he is feeling. You always have to put yourself in his little shoes and try and feel what he is feeling. I am sure it is awful. I know it is frustrating , believe me I KNOW! lol Get a sensory diet going, learn about the brushing system, get him weighted blanket or heavy toy, have him do a lot of heavy work throughout the day. I cannot use timeout it never worked, I have an "uh oh box" I have 4 main things I want worked on that are behavior issues ( sassy mouth, hitting, etc.) taped on the front of the box with these cute little monsters, inside the box are chores, for your son they could be picking up toys, something to help you with, etc. misbehave you pick a chore, have a great day put a sticker on the chart. For my son because he is older ( 8 ) he has to get three days in a row to get a reward. then he can pick out of the rewards, lego minifigure, ice cream, etc. It is the BEST thing I have ever done! These kids love visual aids. I know your son is young but I am sure he is very smart. So you say he is definant well... there you go list what one of his things is that you think he needs to learn how to cope with. It will all be ok, I promise. There will always be something different to learn to cope with, but you are his sounding board and his safe place. Just never let anyone label him a behavioral problem , that scares me the most with these poor kids. they cannot help their behaviors if they are not taught how to cope with them. I make the blankets so if you are in need of one let me know, you can message me.