- Long term fix: try Cognitive behavioral therapy (CBT), an evidence-based form of psychological treatment that doesn't have a lot in common with your usual pseudo-scientific Freudian psychoanalysis where you get to pay a shrink every month for ten years and see no improvement. The main idea behind CBT is to go against the grain, so it's the opposite of bullshit spiritual retreats in Peru to do LSD (no offense). For example if you have agoraphobia and cannot take the bus, your 'exercise' will be to actually take it, but just for one stop, then two, etc, and keep doing that regularly to 'chip away' the phobia without triggering a panic attack. CBT is process-driven so there are quite a few self-help-style books, and you can start working on this by yourself. DO contact a professional if you feel this could work but are blocked, though. Books recommended by the ACBT (they list a few titles covering ADHD): http://www.abct.org/SHBooks/
- Short term fix: I bought a Xiaomi Mi Band 2. It's a shitty smartwatch, and an even worse fitness/sleep tracker. But. But I also bought a third party Mi Band control app (the official Xiaomi one is mostly useless), "Mi Band Tools" that can set an arbitrary number of vibrating alarms/reminders. Every morning I change/customize the alarm vibration to avoid getting used to it, decide what my main task of the day will be (i.e. what "idea" I associate with the alarm when it is triggered), then set that reminder to buzz every N minutes. During the rest of the day, every N minutes I am either already working on what I had planned to do, or am reminded I must refocus right now. It's not something I need when working as part of a team, but for some reason when I'm on a solo project I cannot get anything meaningful done without this hack.
Hope this helps.