Should I be worried I'm bleeding too much?

I am 15, have irregular periods. I put a tampon in at 9:45 this morning after discovering i leaked terribly through my pj's/blankets over the night even though i was wearing a night pad. I took the tampon just 3 hours later because it was leaking and it was all used up. is 3 hours unusually short? should i be worried? it's never been this heavy really