I'm like this.
Horrendously disorganised, although i have worked really hard at it and am much better. I too feel very guilty at not being more productive, and also guilty for feeling miserable sometimes when I have it so easy compared to so many others!
I think I'll be doing OK, and then I'll realise that I've dropped the ball on something important/costly. (eg, forgot to give enough notice to DD's nursery of when she was starting school, costing me several days of childcare I don't need and wont use!)
Weirdly, I can be quite good at organising "things". Like a project at work. I think this is precisely because it doesn't come naturally to me that I have had to develop techniques and made myself really understand concepts of critical paths etc, whilst perhaps someone who doesn't struggle with organisation would be more complacent and assume that all techniques are stating the obvious.
I'm also fucking fantastic in a crisis. Which sounds like boasting, but I am. Especially if something bad has happened; I get incredibly focused on who needs to be informed, how to spread the word to those I have no contact details for, what needs to be done practically, transport arrangements, emergency childcare, who needs what support etc etc. I find it easier to cope with bad news if I can be busy too.
But being organised in my personal day to day life? I'm terrible.
Things that help me:
Everything must be written down on the calendar in the kitchen as well as saved on phones etc.
It needs to be done as soon as something has been booked, not left until later in case I forget.
I will not remember that family are visiting on that weekend in October nor that dh is away with work the next week etc etc and its no use being in dh's phone if I can't see it when I need to! I find it far easier to visualise somehow when its on a physical calendar than when its kept digital.
I have forced myself to get in the habit of checking the calendar every morning as part of my morning routine. I miss far fewer dentist appointments this way!
Also, I try not to take on more than what I can cope with. This is hard as I always want to say yes to stuff and can be quite unrealistic about what I can do.
I get dh to take on his share. eg his family are lovely, but Christmas presents and Birthday cards for them is dh's responsibility not mine. I tell dh when I am struggling and when I need him to do more.
One more thing which I need to do (but have not been good at recently) going to bed early so that I can wake up refreshed with lots of time to get ready and out in the morning. Instead of dragging myself out of bed, with half an hour to leave the house, feeling like shit.