See a psychologist and/or psychiatrist. This is something you can work through. Whatever issue you’re dealing with, there’s people who are very experienced in helping you figure out what it is and how to start dealing with it.
For what it’s worth, you might have ADHD if you’re always quitting or being fired because of an inability to perform to your own abilities. Or you might have some other different issue. But life doesn’t have to be this way. For most people, it isn’t.
Many people are scared of seeing mental health professionals because they don’t want to be put on medication. Getting better doesn’t necessarily require medication, but it might be an option. Not all ADHD meds are stimulants. Some like guanfacine, for example, will just improve your executive function and emotional stability without much in the way of side effects. But no one is gonna put you on a chemical cocktail without your consent, and you are free to say you want to try non-medication options before even considering that route.
Life doesn’t have to be so hard for an intelligent and capable person. If you work through this you can be happier, more fulfilled, less stressed. That can literally mean extra years on your life. You don’t have to suffer alone.
This comment thread is great but beware. People without a mental health issue do not understand what it’s like to have one. They can usually only think about your experiences through analogy to their own normal struggles. Most mental health symptoms, even schizophrenia, exist in some de minimis way in most people. But normal people can’t recognize that the symptoms are so different in severity in people with a disorder that normal function cannot be willed. A normal person is really bored, procrastinates for a bit, and eventually gets it together. They certainly don’t lose job after job at great personal cost to themselves. But someone with ADHD might feel something almost like pain at the prospect of working on a boring task. They might spend hours trying to work on something but just can’t make it happen. Only the intense adrenaline of a new deadline, maybe the third or fourth new deadline for the same task after blowing past previous ones, can make them finally overcome their issues and get to work. That is no way to live, and you don’t have to live like that.
Finally, if losing this job would be a serious problem for you, be very careful what you tell anyone at work. You might want to talk to an employment lawyer. As plaintiffs’ lawyers, they will almost certainly charge you nothing for just a quick consult.