Poor you!
I only have the one DD and half the reason she is an only is because I have spent most of her life exhausted. She is very strong-willed and very probably ADHD, has never required much sleep and has vast stores of energy.
We have had a lot of professional help over the years and while it hasn't been 100% successful, it's given me some good ideas to try and the psychologists have been amazing in making me feel less of a crap parent. I have spent many an hour crying my eyes out over my inability to control my child.
1,2,3 Magic is well worth a read.
Find your child's currency and exploit it ruthlessly. For a while I had a lucky dip bag - used to go to Poundland and buy multipacks of things, then wrap them up in xmas paper and if DD could behave from the school gate until we got home then she could pick a prize from the bag. After a consistent week, we moved to getting a star each day and a slightly better prize for a whole week of stars and so on. Eventually she got used to being better behaved.
She's now 8 and we operate a pocket money system where she can earn so much per day and then gets whatever she hasn't lost at the end of the week. She also loses tablet and TV use for serious bad behaviour.
Routines really help, firm boundaries really help and I have found that the older DD gets the easier she gets - the worst ages were 18 months, 3 and 6.
People who are lucky enough to have compliant children will find it very hard to appreciate how difficult it is to discipline a child who has zero interest in pleasing you, who is hard to bribe and for who consequences hold no fear. The psychologists told me to ignore anyone who tutted, gave me 'that look' or said things, but it's not easy.
It's also very much the case that you end up using your energy on the worst bits - if I told DD off for everything she does that I don't like, then I would just be the endlessly snarky mother. I pick my battles and try to praise the good and ignore as much of the bad as I can.
I really, really feel for you, and I am so ashamed of my pre-child self who looked at parents and smugly assured myself that 'my child will never be allowed to behave like that'.