I agree with Dr Colin that you may be suffering from some form of facial eczema, or that your skin may have developed a sensitivity reaction to acne products you may have been using, which can be harsh on the skin.
The dark marks that you described after acne goes away is post inflammatory hyperpigmentation (PIH). These tend to fade on their own, but may takes months to a year to completely disappear. There are effective treatments both to prevent acne, and treat PIH.
I’d suggest seeing a dermatologist, for the above reasons.
