How long is the best period of time to take accutane?

I am 34 years old, I have treatment with accutane for 2 years but with slowly taken. My dermatologist advised me to take accutane by every 2 days and finish all 18 boxes of accutane then stop it. So, I have to finish the 18 box in 3 years target. If I do not finish it, I have to start from the first box. I had oily skin that made my face not quite good. Is it the normal period of time for consume accutane in 3 years? Since I plan to start family soon, will it impact my pragnancy?

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