Premature ejaculation is the commonest sexual problem among young males. Most commonly it is caused and associated with performance anxiety. When you are preoccupied with ideas of not staying enough in bed and or not satisfying your partner.
You should visit a psychiatrist and need to explain and explore your problem. Medicines like Paroxetine 20 mg during the day or Clomipramine 25 mg in the evenings are helpful. Take them under a doctor's supervision.