not every man *shoots* when he comes. for a lot of men their semen just trickles out. this is normal. don't let porn fool you! the usual amount is a teaspoonful, though you could get a little more or a little less.

guys can reach orgasm from a young age, but it takes to reach puberty before a lot of guys actually experience ejaculation. at 16 i would say you definately should be ejaculating, so maybe you are simply overdoing it a bit. you haven't mentioned how often you masturbate, but if you are doing it several times a day then nothing will come out by the third or fourth time!! your body needs to replenish.

the residue under your foreskin is called smegma.