I have nodular cystic acne. I was on medication like retinoid for 20 days, but still it recurred. Please give me basic tips for this.

The only retinoid. ...That will help is 3-6 months of accutane. See prev answer.
See a dermatologist. Consult a dermatologist. You probably need to continue on the retinoid until otherwise directed. There are other adjunctive therapies as well including oral antibiotics, accutane, and others which may be beneficial for you. These are prescription, and will require the direction of a good dermatologist.
Give it more time . You need a longer course of treatment.