In addition to the other great ideas...
I think there's great value in being part of a giving group - either an official fundraising circle or just with 3 or 4 friends can be a real morale and accountability boost. Maybe meet up every quarter physically or online and share your giving plans. I even know a couple of families that talk around the dinner table every month about where they will give their money.
Its telling to me that this has been the approach of many high-impact people in the past. Will McKaskill formed a giving group at Oxford very early in EA days. The Clapham sect in the 1800s would regularly meet in a pub partially to decide where to put their resources (Anti-Slavery/Prison reform/Animal welfare)
A few individuals can stay motivated to give lots over long periods, but I think the majority of people (myself VERY MUCH included) really struggle to manage alone - and there's no shame in that. Even many who can manage giving without a community could benefit from one.
I also think us that do direct work should be more willing to tell the odd individual story of people that are helped by our work, and through those that give the money. EA is rightly allergic to anecdotes as they are the lowest form of evidence, but if we tell the odd story to help motivate people to give rather than to demonstrate impact I think it can do more good than harm. Obviously this isn't "see or engage the person in front of you" but its a bit closer at least.
First off: On-and-off or not, that's 6 years of donating, even if it wasn't consistent on a monthly basis. I'm sure if you add this up, you could come up with amazing numbers summarizing what good in the world you already contributed to. While the people whose lives you have helped to improve or save are not able to thank you personally for it, it was still thanks to you and it can sometimes help to visualize that. Look back with pride of what you did do, not with contempt of what you didn't!
Personally, I was the same until I discovered EA a year ago, and the central key for me was pledging. I know you mentioned not wanting to feel obligated to do it, but from my point of view, it's a good thing to cement your decision while being in the mindset. I don't view it as a negative thing, but a reminder of the dedication I once had to become less self-centered. Not everyone is naturally empathetic or altruistic, and it can be tough to stay consciously on a more generous path if you're not. especially when constantly being confronted with anti-giving mindsets and opinions.
Even if not committing with something "official", automating the donations can also help. My biggest mistake, so to speak, was that I needed to consciously donate my money each month. This naturally led to skipping and forgetting some without catching up, wildly changing the amount based on how much I currently feel like, and so on. Just deciding on some "minimal amount", setting up a recurring donation and having to actively cancel it to stop makes a big difference.
Another topic for me is trying to keep the mindset alive: Follow the charities, institutions or persons that inspired you or you feel connected with, via newsletters, LinkedIn or whatever social media you use. Seeing accomplishments regularly helps staying in touch with what you donate to, and some also add a bit of emotional flavor so that you don't just see numbers, but the actual impact campaigns have.
It can also help to re-read or re-watch what inspired you initially. e.g. I love going through Peter Singer's works from time to time because his writing style resonates with me and puts me back into the mindset I had when I decided to pledge.
Last but not least, if you feel like it, joining communities can also be incredibly helpful to have role models, feel connected, and just encourage each other.
With all that being said: I absolutely feel your struggles, I've been dealing with the same for years and only time can tell how I will feel about the pledge long-term. In my opinion, it's okay to not always be enthusiastic about being charitable - finding a minimum and sticking with it always felt worth it in the end for me, though. It's usually the fear of tomorrow that makes me unsure about it, but when looking back I never once thought "if only I saved the money I donated for x...". Instead, it's "I'm glad I was a part of this".
Thanks for pointing out that I have been doing a lot of good already! I feel like I should go back and tally up my donations to see how much I've done. That'll probably help me feel like I've done something.
I'm seriously considering the pledge. I think the donations I made throughout the years felt inconsequential. Perhaps it's the amount I donated each time, and/or that I never tracked if I ended up saving a life or not.
Good idea to follow the charities. I wish GiveWell or those other charities did something similar to GiveDirectly where they actual record photo/video of the people you're directly donating to. I've made the choice to still donate to GiveWell just because of the cost-effectiveness to save a life.