I agree that the most likely diagnosis is post inflammatory hyperpigmentation (PIH). This usually occurs when the initial acne is red and inflamed and the acne settles leaving the unsightly marks. Squeezing acne is best avoided as it tends to leave more PIH.
PIH will usually fade with time but it may take weeks or months for it to gradually lighten. Some creams like tretinoin cream and hydroquinone may help it to lighten faster. Chemical peels may speed up the lightening too. From your description, it does seem like your skin is a bit sensitive. Some of the above treatments may irritate sensitive skin so it is best for you to be evaluated before using them.
It is important though to make sure that your acne is under control so that as the old marks fade, you will not be left with new marks.
