Why'd my cycle change?

Gwen
I just turned 16 and my cycle  recently changed from 30 days to 29 days a couple months ago. I was ovulating Every month before but I don't think I ovulated last month and I thought I wasn't going to this month because the app says I only have 3 days left but I just got the clear stringy discharge that I'm supposed to. I'm paranoid that something may be wrong so I just wanted to make sure this was normal for my age and ask if anybody knew why my period would change now?