I agree with lonegal, it would be good to check for any physical condition.

I dunno if it's SAD or not but weather can effect everyones mood! If you're feeling a difference with less sun, maybe you should look into some light therapy to help with this. I personally have a full spectrum light bulb. It helps a lot (though for me not enough to "fix" everything). I'm looking into getting an actual SAD light.

The way I see it, it's always worth a shot. Full spectrum light bulbs are not much more expensive than normal ones - you could try this first and then if it helps you could see if you can afford SAD therapy light.

hugs to you