I think what you are feeling is pretty common. Grief is not linear. I think CANDC's analogy of an onion is a good description.

I see you are in the US. Where I am it is summer, but I grew up in the US and January-February always seemed to be a gloomy time of year even if I was not dealing with other stressors. The holidays are over, the days are short, the weather is often bad and it can be hard to get out of the house. I wouldn't be surprised if that was a factor too.

Hugs to you. I hope you're doing better soon.