>Any ideas about how to turn this into a daily habit?

Pill box, either at breakfast or the office, or similar. It's worked well for me for the last two years, with a mixture of vit D, vit C, omega oils and the like.

I was able to develop the habit of taking supplements by attaching them to a craving and replacing an existing behavior. When I feel hungry or eager for a snack in the early afternoon or late morning, I know that means it’s time for a small glass of V8 and supplements. It’s worked well attaching it to a craving like that as I am not actively trying to remember to take the supplement, I am just triggering it off of something that happens every day anyway.

Make it part of your routine. Put them in bathroom medicine cabinet and take right before brushing your teeth at night. Or if you do regular breakfast, take with breakfast.

Tie it to an activity you already do daily.

While vitamin D can help with sleep overall, I've read that vitamin D can temporarily interfere with melatonin production immediately after ingesting. So you shouldn't take it at night, too close to bedtime.

Of course, I've also read many people take it at night with no negative effects – and that, as a hormone, it absorbs more efficiently overnight in a sleeping state.

So, this is probably one of things that affects people differently, but it's just something to be cognizant of. If you take it a night and feel restless, try switching to the morning.

I also have a close friend who gets severely constipated with most vitamin D. It took her a lot of trial and error to find a brand that did not constipate her, which I cannot remember right now.

Gwern has done some self-experimentation and found Vitamin D to negatively affect sleep https://www.gwern.net/zeo/Vitamin-D

I was told don't drink coffee for an hour afterwards as it reduces the effect.

In young males like you this condition is quite rare unless you are an astronaut, isn't it? (edit: assuming you are male, sorry if mistaken)

Vitamin D deficiency is common at higher latitudes (Bay Area is at the border) and as you get older. It can cause fatigue and aches. It is diagnosed through a simple blood screening.

Indeed, I am male, and this is very rare among males (or females) of my age.

Look into vitamin K2 for calcium regulation as well.

Tape the bottle to your toothpaste.