Getting a sustained erection and ejaculations there off is a matter of complex inter play between a human psychology and physiology. There are hindrances like anxiety, depression, stress, smoking, alcohol, medicines etc that can hamper a normal sexual health. If these are addressed and the problem persists, we usually check for the seed hormones. If you have masturbated successfully then you must not have problems in having sec with your partner. It means that your physiology is intact. However, of there is lack of libido, energy and easy fatiguability then hormonal balance should be checked. The role of antidepressants and Antipsychotics come very late. In case there is no erection or poor erection, drugs like sildenafil may be of help. Must consult a doctor who is dealing with this issue