Worried about irregular periods?

all i know is that last month i came on on the 12th, the month before i can't remember.. but i still haven't come on. i'm not pregnant because i've not had sex. i don't and have never taken 'the pill'. my periods are quite irregular and i'm starting to worry. i have signs that i'm due, 'cause i get real bad spots and i have had them for about 5 days. btw, i'm 14 and have had my period for about 3 years. it's always been 1-3 days off, (3 days has only happened about 5 times) anyone else have a dodgy cycle? should i be worried?