I don't know how big or small is your penis. However the average size of penis when erect is somewhere between 4 to 6.5 inches. Your penis is not a cloth that it'll shrink. If you have any questions about masturbation let me tell you it doesn't cause any harmful effects on the body or penis size. It's all a myth. About ya foreskin if it's too tight and painful and not getting back the best thing you can go visit a doctor and let him be the judge of your problem.