Exercise your pelvic floor. You may not be able to build up the penis itself through exercise, but if you strengthen your pelvic floor your body will be better able to hold blood in your penis. The pelvic floor presses on the vein that keeps blood from leaving the penis during erections. You can strengthen your pelvic floor using Kegel exercises. A trial conducted in Britain concluded that men who performed Kegel exercises experienced better sexual function than those who made other lifestyle changes but didn't perform the exercises.
Some men seek injections of natural and synthetic fillers to increase the girth of the penis. Others seek surgery if a smaller penis size or penile abnormality (like hypospadias) is interfering with the ability to urinate or quality of life. Small penis size usually is not an indication for surgery to treat infertility. In such cases, assisted fertility procedures may be the better option.