It takes time. You have to throw out the rule book, unlearn everything you thought you knew about children and start again
But it isn't you, it's never been you and it's never going to be you! It's just the condition.
And it is tiring when you're not doing well yourself. I've got fibromyalgia (among other things!) and when I'm really bad, I have a lot less patience - because I'm exhausted and I'm in pain. It's hard to get stuck in there when you're in agony. You need to be kinder to yourself, Thought.
And forgive me for saying it, but your husband needs to realise this is going to need to be a team effort and not be 'leaving you to it'. This needs both of you right now.
Your username - can I assume you've lived through the Ben10 obsession and are currently suffering pokemon?
You have my sympathy. There is a box full of every ben 10 toy known to man (including the rare gwen10 figure!) to go with the full set of ben10 cartoons that had to be shipped over from america and a multi region dvd bought in order to play the buggers and it never gets played with, none of it.
Same with the gogo collection of hundreds. And the box of cars that contains at least one of every make and model of car in the whole bloody world. And the gormiti. And the pokemon...
The collection must be completed. While it is under completion it is the only topic of discussion. As soon as the final piece is in place - it is instantly discarded.
This is early days for you, and everyone is different anyway, I can only tell you what works for us. We laugh. We find a way to keep on laughing. We've got the "2" song (echolalia/verbal stims The Musical
) me and my husband use some of their phrases to each other
NEVER mockingly. NEVER when they can hear. Just between ourselves as a way to laugh. You need the humour. The black humour. It keeps you sane.
I'll never forget being on my hands and knees playing hunt the poo, or the time we walked into their room to find my eldest had covered his face with his own poo. Laugh, laugh, laugh! "23-19" yelled out meant BRING THE CLEAN UP STUFF. WE'VE GOT A POO EMERGENCY!" (from the decontamination scene in monsters inc)
I sound like the Poo Troll 
Now, I respect that that won't work for everyone, but for us it's always helped. Made it all less of a monster situation to deal with.