Confused about OPKs

Z
Hi ladies. Anyone else using OPKs? This is my first month using them so I'm not too experienced. My fertile week started on the 13th according to Glow and I thought for sure I'd have a "smiley" in the digital display today since it's the 15th and Glow said 17tg is my peak.... BUT still not! Any idea what that means? Do you ALWAYS surge? I'm confused...thx