Once the season changes and it gets cloudier, colder, windier and less sunny if you go from getting sun, going on hikes, running, biking, walking, etc to hiding inside and not seeing the sun for months you're gonna downslide into depression. I know this as a Canadian experiencing fall/winter every year.

What I do is the following:

1) Vitamin D3 supplementation starting in October and ending in April.

2) Keep getting outside for activity no matter the weather (dress in as many layers as you need to).

3) If temperatures are even slightly above freezing (celcius) and there is sun out (like today) I'll wear three or four tshirts and a thin hoodie with the sleeves rolled up over some shorts and no hat on my head and then I go outside and soak in an hour or two of sun. If there's not a crazy wind and the sun stays out you can actually tolerate the temp in shorts fairly well (need the layers up top though; one tshirt is just not enough).

4) For windy days, if you have a garage or a room in your house that gets a lot of sun you can sit in indoors with an open door or window and soak up the sun while avoiding the wind. For me my garage faces the sun in the morning/early afternoon and I have privacy in my yard so I can just strip down and chill in the garage for a while feeling somewhat like its summer (sun constantly on you) while avoiding the raging winds.

Also, for year round, and this goes for all guys, if you can get privacy and sunshine at once, expose your "boys" to the sun at least 10 minutes a day (I aim for 20). Sun exposure on the genitals stimulates male hormone production.