Sounds like you are having palpitations which is bascily a skipped or dealyed beat. They are not life threatining but you should schedule a visit with your regular doctor and get a checkup and let him know whats going on. Don't concentrate on it too much , try to keep your mind occupied on something else. Don't need to cause yourself any unnecessary anxiety over it.
I'm 21 and went thru the same thing just recently except I had alot of anxiety on top of it.
Also you can read this thread which explains alot about it: