Despite any ads you hear on TV/Radio/Internet there are very few viable treatments for small penis other than drug therapy such as Viagra or related drugs or surgery.
Also understand that these drugs do not increase the size, only the ability to achieve and sustain an erection, and understandably these are temporary.
Unless your penis is less than 2.54 centimeters when erect, that is 1 inch in length, mechanically you have enough to be effective for reproduction.
If you are less than say 22 years of age you may not be done growing. If you are having these issues you may be dealing with hormone levels below where they normally are. a good health provider can help you find out if that is the case. and then you can work together to find best treatment choice for you. As mentioned surgery is also an option but not without risks.
webMD as well as the Kinsey Reports