No idea where to put this thread, a bit special needs, a bit primary education, a bit Total Meltdown section but couldn't find that one so I've put it here.
Anyway here goes. We are not in UK btw
DS is 6.5 and challenging with a capital C, always has been. Changes in his life this year have been 1) DD3 born in Feb last year 2) he started primary school in Sep last year. Behaviour always difficult, very disobedient, rebellious and seems not to care that he upsets people. Unpredictable and hasn't learned anything about e.g. road safety despite my best efforts which means my nerves are always on edge when we go out.
I've tried being patient. I've tried not insisting about vegetables. I've tried being consistent and other people have also told me I've been consistent but he just continues being obnoxious, mostly to me and DH. I've tried giving him own space and making sure he has "own" sport (that he asked specifically to do and then two months later just gave up), asked a friend round from school but it's just no no no all the time. Don't want to go to school, not doing my homework, don't want those trousers, this food is disgusting, all day every day.
So in December we started an "assessment" process, gave him blood tests but nothing wrong there, am giving him vitamins. Where we live there is a 1-year wait for a health service assessment so we are now paying a child psychologist privately. Had the first "report back" interview with her 2 days ago, she seems to think he has issues with being middle child (DD1 is 8) and doesn't know where he fits in. When asked to draw a picture of his family he drew 3 figures (but there are 5 of us) all standing very close together but all male, and changed DD's name to a boy's name 
. She also said to worry less about trying to give him good manners and make mealtimes "loving and caring" and about "being together". She suggested seeing him once a week to "give him space". When told that the lady doctor wants to see him again he just said "no I'm not going it's stupid". Everything is either stupid, boring or disgusting.
This morning again it's more negativity, not going to school, why do I have to go to school, you and DH can do what you like (!!!!!) ...
Me and DH are at breaking point. I have no idea what to do or what to say to DS any more, anything I do say is wrong. Last week I had a total meltdown (in front of DS and DH), kicked the dishwasher and threw things round the kitchen, now I feel like a complete failure and even worse than I did before.
In the meantime there is DD1 who is getting sidelined and I also feel guilty about that. DD3 miraculously is a little ray of sunshine.
So the only thing I can think of now, apart from continuing to see the psychologist, is to change schools: we sent him to DD1's school - not the most convenient choice for us - because there are a lot of problems with overcrowding, bad organisation, lack of facilities etc. at our local one (another child we know has since moved from that school to DD1's school due to these same issues). Trouble is DS's best friend goes to this crap school and DS obviously wanted to go there as well. We said no. I reassured him he would make lots of new friends but that doesn't seem to have happened. He has 1 and says the other boys in his class are "not interesting".