How do I know if I orgasmed?

Okay, so I'm almost sixteen and I, like most teenagers, am a horny mess. I've masturbated since I was like ten and I do it frequently, but I'm not sure if I've ever actually orgasmed. Sometimes it feels so good that I can't continue, so I thought maybe that was it, but when I asked my girlfriend and close friends about this, they all said an orgasm is different and you just KNOW when you orgasmed. So I'm still pretty confused. Is there anyone who can explain it to me? How do you know if you orgasmed?