I'm so confused!

Wendy💋 • Mommy to 4 sweet babies. 2 beautiful girls and 2 handsome boys. My heart is full.
Glow said my fertile a down STARTED today. 
I took an opk and it had an immediate smiley. No flashing (which means I'm at my peak of fertility) 
My period just ended on the 18th can people really ovulate this fast?