Is it normal for cycles to suddenly become much shorter? I'm 16, have had my period since I was 10 and after a year or two of irregularity it's settled down into a very regular 28-30 days long cycle. My previous period came 2 weeks early, but lasted for the normal 5 days. Now I've got my period again, and it's 1 1/2 weeks early. I'm definitely not pregnant, not on any birth control and I haven't had any major weight changes recently, so I don't know what's causing this. Is it something to be worried about or will it just settle itself down again?