I personally just felt a little sadder and lower energy in my first winter in a gloomy climate. The vitamin D just made me slightly more chipper and energetic.

I didn’t do a blood test pre vitamin D but tested recently and my levels look good, so my doc said to just keep on it.

Wouldn’t say the difference is transformative but it’s helpful.

How are feeling generally? It's possible you didn't have a deficiency to start with. I went from being completely depressed, barely able to get out of bed to mostly functional (although still not quite as chirpy as I am in summer) when I started taking a vit d supplement in winter.

you might want to check on your Vitamin D receptivity. For example, I took a DNA test, and it indicated my Vitamin D receptors weren't as efficient as normal so I should take higher doses than other people.