I can't get my foreskin right back?!

I can't get my foreskin right back?

Is this common, my foreskin won't go all the way past the head of my penis when i have an erection, i'm 14 btw

Yes it's normal. Some guys have really long foreskins that cover the head even when erect, and others have shorter ones that only partially cover the head when flaccid. Some guys have tight ones and others have looser ones. How long your frenulum is (the little piece of skin underneath the head, that connects the foreskin to the shaft) determines how far back you can comfortably retract the foreskin. If you have a short frenulum, it doesn't go back as far, if you have a long one, it can go back all the way to the base of the penis. As long as you can retract it enough to clean underneath it and experience pleasure when masturbating (or during sex), you are fine.

There are stretching excercises that you can do to make it looser and to be able to retract it further. After a warm shower/bath, stretch it all the way up and all the way back as far as you can (comfortably) every day. Eventually it will get looser and easier and easier to do. If you have an extremely tight foreskin, you can talk to a doctor and ask about topical steroid cream which is designed to loosen up the foreskin. Just don't let him talk you into a circumcision (unless that is something that you personally want) because 9 times out of 10 it isn't necessary at all. Always get a second opinion before making a decision like that. But I imagine the stretching excercises will work just fine for you.