These could all be down to dyslexia.
You could get a private diagnosis and you will get one, my gp friend says everyone who pays a private doctor gets a bit of paper with their desired diagnosis but they (gp's) know that they are not real hence many settings not accepting them.
Think about what you want to address, day dreaming? That's common, not a medical concern, obsessing- is it at inappropriate times, is it ruining their life? Some people are naturally more obsessive than others and it's not a concern unless it's interfering with normal life (I'm sat next to a man obsessed with aircraft, it really is a non issue). Meltdowns - contrary to popular belief, kids don't stop having them at 4, they lessen but it's quite normal for children to get really upset, I certainly did at that age, and right through my teens I could be a right madam!
I think what I'm saying is that perhaps you and society more generally needs to stop trying so pigeonhole people into a binary of "normal" and "neurodiverse" it's a continuum and many people including myself, my husband, one of my dc, my exh, my brother and many more in my life sit in that middle ground, and we function in society just fine as long as people will leave us alone and not make us conform to certain norms, so what if I obsess over things, it's just me! (And I'm a right daydreamer too).
To get a proper diagnosis it needs to be observed in two settings, just think about why you want this? For medication? I would hate someone to have drugged me to make me conform. I have an autistic child and it was very apparent from weeks old that she was different, honestly you know if they are autistic to that degree