i understand how hard it is, DS1 (16y) is ADHD and it has been sooooo hard, some days were worse than others - but TBH none were 'easy', DS2 has problems of his own too, DS4 is going thru tests, and DS5 is autistic but only 2y atm, so not that horrendous yet! and at least 2 of them are coeliac too... Im not trying to 'outdo' you, i just want you to know that you are not alone.
Eventually the one thought that kept me sane and that i clung on to was "this is NOT personal, this is how HE IS" I think the worst years were when he was 8y, i really could have either punched him hard but i didnt i hasten to add! or given him away, which i didnt do either - but now he is a fabby chap to be with now hes come thru 'the other side'.
the only other life saver I have is something that I look forward to EVERYday, wether it be a jigsaw, a magazine (bit expensive) a book, a soap on telly (tape it if need be). MAKE SURE you get YOUR 30mins that you can look forward to, whatever it happens to be. so even at the worst point during the day, you can grit your teeth and look forward to 'your reward' because you are a good mum, you must be otherwise you wouldnt care, or be asking for help. And a slightly bigger treat once a week: going shopping on your own, bubbly bath with candles, film and chocs, curry night! again whatever... so that when the daily treat looks like its not enough tho it will do for the time being, the weekly treat will still be there - and dont be fobbed off thinking, ahh well maybe I'll do it next week... YOU have been a good mum all week and YOU DESERVE IT!
Like others have said, it will get easier, and you will be a stronger person for it. A lesser person would not have coped so well, and your children are lucky to have you.
sorry to ramble {{{HUGS}}} for your journey.