This could be due to ADD, I am still getting tested. Granted, that's a diagnosis, not a root cause.
No, it’s a diagnosis
of the root cause - in fact, it is plausibly
the root cause of everything else described in the post. Inability to complete work, procrastination/distraction by focusing on nearby tasks, the pervasive sense that you struggle with things that other people do not, even the depression (untreated ADD causing repeated failures, repeated failures causing depression). To understand why it really could be the root cause, you can read up on “executive dysfunction”, which is what ADD really is.
The treatment for ADD is one of two medications, methylphenidate or dexamphetamine. You can try other things in addition to these, but not instead of these, and you should try both - there really is just no substitute.
(In some places, bupropion can be prescribed as an antidepressant. It has effects that also help with executive dysfunction, so you may find it to be more effective than serotonin-based antidepressants.)