What the heck? Any advice?

Had a 31 day cycle april-may, 29 day cycle may-june a 29 day cycle, and June to July a 28 day cycle. Ovia says I start on the 12th(29 day cycle) and then glow says 13th (30 day) my cycles used to be 31-33 days long for a long time and I don't know what to think. I look on Google and all it talks about is menopause and I'm 19 that seems a bit early so any opinions would be appreciated I know it's probably not major but I'm curious ☺thx