Hi!
Usually changes that are rapid are more likely to be something simple such as a yeast infection, although I would expect you to have some additional symptoms. Premature menopause is unlikely to present this way. Pregnancy could OR a condition called acanthosis nigricans which is seen in PCOS patients. Neither seems to fit your bill.
If you were my patient, I would ask you to wait and see if things improved spontaneously, or if new symptoms developed that would make it more clear what's going on.
Good luck!
Dr B
*Edit: Could this be premature menopause?