This is, purhaps, one of my biggest obstacles.
When you're not in the habit of writing every day, it can be quite the challenge. Even when I do write, I don't always write on the same project. As my days become scrambled or blurred together, I find it difficult to recall which project got attention on which day.
I track my progress as I reach each new point in my writing. Thankfully the program I use to write on my computer with, will track the date last saved. I tend to write as I'm inspired to instead of being more structured. This is something I'm working to improve upon since I feel it will assist my regularity. And who wants to be irregualar? Certainly not me.
We need to keep in mind that time isn't going to stop. It may slow or speed up at times, but it won't truly stop. We simply need to make sure that we are taking the steps we need... make sure that WE aren't stopping either. How?
Write something every day!