Why did my period come 4 days early? I have a short cycle anyway so I get my period every 20-21 days, but looking at my <a href="https://play.google.com/store/apps/details?id=com.glow.android.eve">period tracker</a> on here I just got my period 17 days ago. The only thing different I've done is I've been miconazole for my yeast infection, could that change my cycle? I'm not on birth control or anything like that either.