never turn to medicine just because you cant get erect.
1)find out the root of your problem.
do you smoke,have sex constantly, or watch porn and masturbate alot?
I may suggest some light exercise also.
Male deer exercise,
Sat kriya
kegel exercise,
circulating sexual urge around microcosmic orbit,
Deep and slow abdominal berating.
If you are prepared to 100 days practice, you may follow a book, 100 days practice for good health,Better sex and Linger life. You will find few chapters In amazon.com .This book has the ability to change one's life.
If you inclined to yoga, you can do kundalini yoga. Learn it from a teacher or from any website.
If you have a very cooperation girl friend and the patient one, you can do this experiment. This sex therapy is suggested by a sexologist. You have to change your goals. You have to take baby steps. In the first stage get the penis just touch her vagina and keep it there as long as possible. Second step can be just enter vagina.In this way you get accustomed to reach sub goals and eventually when you are confident, you may plant to full intercourse. This is brief narration on sex therapy.