I've had this problem for a while, when trying to get erect, my foreskin stretches so much and becomes super tight between the top of my gland and the bottom, just about the middle. I can't pull it back because it hurts and it tight. The back head of the glands where the foreskin is attached is also tight and pulls quite hard.
I've tried using lubricants and stretching using several techniques to make the foreskin cooperate, so longer and/or the hole wider.
I believe this could also prevent me getting "fully" erect and to the max.