How old are you, what "time of the month" is it for you?
I'm 66 and still have a hormonal swing -- why didn't anyone ever mention this possibility/likelyhood after menopause?? -- a swing which I can recognize to the hour every month.
If (probably!) you still have your thyroid, pituitary, adrenals, and such, you still have "hormones". Some of us are just more sensitive to the effects of them; apathy/depression/fatigue/lethargy can definitely be a part of that package. Generally I don't fight mine, I just go with the flow...some days I'm the dove, some days I'm the statue covered in bird ----.
Keep a calendar this year and compare it next year to see if weather or day of the month is what you are experiencing.
Jan in VA