Hi.. A normal size of the penis when erect is between 3.5 inches to 7 inches.. So if your size in an erect state is between this then it is normal.. There is no medical treatment described to help in increasing the size of the penis.. If you find difficulties in sexual life, drugs used for erectile dysfunctions may help in solving the problem.. Fore skin can be excised by simple surgery known as circumcision.. You can get this done...