If motivation is a problem, I'd say set aside a brief period of time (10 minutes?) and set a timer if you want. It might make it seem like less of a chore.

I journal every day. Sometimes twice (or more) a day. There have been times when it was strictly mood/sleep/weather type stuff. Other times I'll get more in depth with what's bothering me, or maybe make a list of positive things I've done that week, or just more detail about my life. Lately, I've expanded to writing about specific traumatic events. These days I probably write 6-8 pages.

For me, I find that getting my thoughts on paper in and of itself can make me feel better. If it doesn't, at least I know that keeping track of moods, symptoms, triggers will help me in the future.

Try a week or two of 10 minutes a day (I find first thing in the morning, with my coffee, or at night before bed are the best times) and see if it helps.