My 4 year old cries at the drop of a hat and has frequent meltdowns

I have a 4 year old and I have no clue how to handle his big (huge) emotions. I’ve googled it and he might have an emotional dysregulation? 2 Examples:

• I brush his teeth and in the middle of brushing his teeth he says he wants to drink water (he cries immediately the first time he said wants water). I tell him you can have water after we’re done brushing your teeth, we’ll be done soon, and he cries even more with toothpaste in his mouth still that he wants water NOW! Then after he got his water he realises dad isn’t next to him so he cries again because he thinks dad is already in his bedroom before him and he hates ‘losing’. He wants to get there first. Anyway we know this about him and dad is in the hallway waiting for him.
• he went to the library yesterday to borrow books and tonight at dinner time he demands we go to the library again NOW, we told him we will go another day / the next weekend and that it is dinner time now and too late to go. He cries and has a meltdown for at least 15 minutes. It is to the point I’m not keen to take him anywhere fun because then after that he will make that into another cause of a meltdown in the future.

In general, I want water, cry I want to play a board game, cry I lost a game, cry I knocked my tower down accidentally, cry I want to turn my AC on, cry And so on and so on

With the game, him losing and crying, ok I get, I can teach him that losing is okay, hopefully he gets it but why cry when he wants water? It’s right there nobody’s going to say no, why cry when wanting the AC on, nobody has ever said no???? Most things are followed by crying or saying it with tears.

If he wants something he wants that NOW, i’ve tried giving choices (2 choices so he doesn’t get overwhelmed), it doesn’t work he stays fixated on what he wants NOW, i try telling him after we do this we will do that, it doesn’t work either he is fixated again on doing whatever he wants to do NOW and he will repeat repeat repeat whatever that he wants NOW over and over, goes into meltdown for 15 minutes 30 minutes 45 minutes, unpredictable. And it’s not like I give in, I don’t give in, I stay firm and yet he is so fixated on what he wants when he wants it that he doesn’t hear anything I say.

Last one is car meltdowns, whenever he wakes up from a nap in the car, he will cry and scream and be demanding water, when given water won’t drink the water and will keep screaming and crying he wants water. When he breaks out of that he will say he wants to stay in the car then he wants to get out of the car then stay again, he wants to check the mailbox, he doesn’t want to check the mailbox, a looooong back and forth of crying and screaming wanting this not wanting it for at least 30 minutes-1 hour. I try keeping him awake in the car but it’s not always successful if the trip is a longer one.

Also, we got to the point that we never tell him plans anymore until when we are going somewhere right then and there because saying we’re going to the mall tomorrow or we’re going to see this friend next week, or we’re going to x event in 2 days, he will say he wants to go NOW and has a meltdown from not going right then and there. so we keep it to ourselves until we are about to go.

I can say a lot more but I feel like the post is getting too long. HELP, I’m losing my mind, is this normal? Should I be concerned? Is this possible signs of autism/neurodivergent? Or is he just a difficult but normal child? Any insight/ similar experience would be appreciated, TIA