I used Accutane 2 yrs ago 20 mg for 3 months. I am 48 kg. Just now acne appeared again so do I need a second course?

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.

First, there is no way your original round was enough for a long-term cure. Most people need between 8000-16000 total mg. If you took 20mg for 3 months, you took 1800mg total, not nearly enough for a long-term cure. "This answer has been solicited without seeing this patient and
cannot be held as true medical advice, but only opinion. Seek in-person
treatment with a trained medical professional for appropriate care."