When I Was 16 My Dermatologist Have Prescribed Me Deriva

When I was 16 my dermatologist have prescribed me deriva and after applying around 15 days it went fine. Now I m 20 and again I have pimples so I started using deriva from yesterday night. Before that since three days I was applying vitaminE and my skin was bit improved by it. Can I apply deriva at night and vitaminE in the moring??? Or can I apply both at bedtime keeping interval?? Or I stop using vitaminE until I stop using deriva?? How long should I apply deriva ???