Fine getting erection, problem keeping full hard erection

I'm mid 20's, male, excercise daily and don't smoke, drugs etc. but i am having problems keeping a full and hard erection.

In relation to getting erections i have no problem, i frequently wake up with an erection, can ly awake in bed for hours with an erection when I thinking arousing thoughts however when either i start to masturbate or have sexual intercouse the full hardness reduces a bit to a more semi-erect (more pointing forward and semi-hard instead of pointing straight up and hard).

I remember i did not have this problem years ago and it would stay rock hard the whole way through but now it seems to die off a bit. If I stop stimulating and pause for a second or two my erection will build up again and become more firm and hard. It's really annoying b/c I use to be able to constantly masturbate for at least 15-20 without any reduction but now even after a couple of minutes it seems to back off a bit. Now I'm not saying it goes completely flacid it just loses it rock hardness.

Could this be some medical issue? i am pretty healthy and fit but i am bit worried.

[palpateit]

do you, have you masturbated to internet porn?

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[Me288]

While having intercourse I'm not able to stay erected this the first time it has happen to me it's been going on for about to be two weeks any help