Why am I still having acne and oily skin 2 years after using Retin-A?

i've used retin a for almost 2 years now , i had light acne on my cheeks and front , by using tretinoin my skin improved a lot but i still have some pimple sometimes , also I started having very oily skin, when I say oily I mean that through the day my skin goes to dry when i wash it to super oily after some hours, i have pretty clear skin but I'd like to minimize this problem .

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