You are not alone!
Sounds like you might be taking too much stuff on for each day…? Maybe there are some less important things that you can ignore?
Would it help to have themed days? Where you focus on tasks that are related? My projects are quite varied, which is nice, except that it takes me quite a lot of time to switch. Having themed days removes this changeover cost.
I try to use a timer to get up and away from the screen.
I ignore email until about 2pm, when I’m staring to flag. If things have gone ok that day, I’m usually keen to get back to the main project and I just want to get in and out of my inbox ASAP. I used to head to my Inbox first thing. This was terrible for me BC I’d spend ages writing long perfectly crafted emails. I find email rules helpful to send to specific folders. The mail in each folder will be more-or-less expected and I can archive/mark for action.
I try to plan tomorrow around 3-4pm. I’ll look in Omnifocus/Reminders, etc and drag into my Calendar. If I’m theming, I might put a job into a particular day later that week.