After I masturbate a few times (three or four times in one day, or even if I do it only once a day for three or four days in a row), my foreskin gets really sore, and it hurts to masturbate. It also turns red on the very end and appears to have little cuts around it. The foreskin slides back very easily when I'm not erect, but it is tight when I am erect. What can I do to stop this from happening, other than not masturbating?
Your foreskin is probably too tight. There is a simple procedure a doctor can perform that can greatly increase your comfort; it involves making a slight incision in the foreskin. (Whatever you do, do not try this at home!) In the mean time, though, try putting some Vaseline on your foreskin before masturbating. That might help to keep it from becoming irritated. In the mean time, apply some first-aid ointment, like Neosporin, to help it heal.