ITT people mentioning bipolar disorder but I would suggest a strong onset of Premenstrual Syndrome (PMS).
My only question to you is, when did your menstruations start this month? You don’t have to reply to this.
But look up whether they started the day you were sad, or one day/two days prior.
If it was the case, it is very likely PMS.
Keep a calendar of your cycles and you will know.
Causes of PMS may be one or many, like birth control, undiagnosed depression, a stressful time, etc. etc.
Edit: typo

I love the vibrance of the colors in this one

Her boobs are too long. Try to end them up higher. Her left eye is off, I’m not sure how you should correct it.
Besides that, the painting is good, the colors and shadowing are good. Nice!