Just use a Calendar... and write somewhere what you need to do. Or hell, just use your brain, if you can't keep what is important in your head, it probably means it isn't important at all.
Your life isn't complex like managing multiple workstreams and projects for a whole organisation of thousands of people, it's supposed to be simple. If you have too many things to keep track of, you are doing something wrong.
People like to overcomplicate their lives. Just do it!