My kids are exactly the same. I have a 4 and 7 year old, the 4 year old is constantly on the wind up. Copying me, his sister and father in a winey voice, hitting, spitting, biting - you name it, he probably does it. With the 7 yeat old - the tantrums can be pretty full on.
Lockdown hasn't been kind to many of us, especially the kids not in their usual routines. But I put their bad behaviour down to attention seeking. If the 4 year old starts playing up (it grows throughout the day so we can tell!) We do some 1 2 1 time. Something he can control but an activity together - puzzle, lego building playing with cars where he directs me to go. Doesn't have to be long just long enough to get him engaged and usually he will continue the play alone. If I can see he is lazy, ill read a book to calm him down. Its like he wakes up so energised and he needs an outlet to use it all.
I'll do the same with my daughter too, I think my son gets a little competitive and they end up playing off each other and snitching on silly things (mummy mummy, X didn't clean up her room, X didn't put his toys away ummmmm and then it turns to WW3!). Drives me insane!!!
Obviously we discipline if its too much - time outs and removing tablets/TV/console privileges. Consistency is key here and you are your partner need to follow through on any punishments if they cross the line.
I'm just giving you my experience of my kids, I get it is super stressful at times but school does start next week and I guess that is my saving grace. I have suffered quite badly with my own mental health and been seeing a counsellor for 3 years. If you feel you can't talk to anyone around you, the NHS offer counselling (at the moment its telephone based and the waiting list is long) but if you can afford it I would recommend it. It does help take the burden off and you can talk as openly and honestly as your heart wants with no judgement or interruptions. I now seen things in a completely different way from when i first started, although I still have my down days and drop in when I feel I just need to talk to someone.
In addition, it is so important for our own mental health to have some space sometimes. Would you be able to have a day or 2 a month where you just do whatever you want that makes you happy? I like being by the coast, so I go down with my family and sometimes alone when I know its not going to be a big disruption to my husbands day by leaving him with my kids. I havent done it in a while because of lockdown but I intend to go in a couple of weeks when they are in school. I'll just sit in a cafe opposite the sea and watch the world go by (it is effort as I live 2 hours away from the nearest coastline!)
I also recommend exercise - it is so good for not only physical but also mental health. Going for a walk or run outdoor with the fresh air, or a bike ride can do wonders. To escape the madness of the house for an hour or so.
I hope you start to feel better soon, but just know you're not alone. Kids do things that wind us up, i know personally I was a nightmare as a child! Feel