Why does acne become worse with the first use of isotretinoin?

I don't usually get pimples but this year a lot of white heads appeared in my cheeks, and few pimples im my foreheads. And when i showed it to a doctor he pescribed me isotretinoin and few topical medicines. Now its been 1 month that im under medication, my skin has become worse, cystic acne all over my lower cheeks, which is really unexpected. Is this normal?

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