I'm taking Isotretinoin 20 mg a day and have Erectile dysfunction. Is this normal?

Yes, unfortunately Accutane can be very expensive.  Talk to your dermatologist to see if they know of specialty pharmacies in your area that can get it for you at the best price.

I think you should have been on Accutane for at least 20 weeks to get the maximum benefit.  You were also on a very low dose, and maximum efficacy of Accutane is 20 weeks of 0.5 - 1 mg/kg per day.

Usually the only time I put people on long-term, low doses is if they have already completed a full regimen. So I would do as your derm suggests and go with the 6 month regimen and then maybe go on a long-term dosage after that as a form of "maintenance". "This answer has been solicited without...

You need to have a lot of patience when treating acne redness and scars.  It may take at least 6 months to get a significant improvement!  You should consider chemical peels and/or laser treatments but long after you've stopped your Accutane therapy. 

There is no good published data that Argan oil has any benefit.  As an MD, I rely on evidence-based medicine when recommending a product or treatment.

I think this dose was too low.  You need 0.5 - 1 mg/kg per day for at least 20 weeks to get maximum efficacy on Accutane.