Positive opk 4 days before my period is supposed to start?!?!

💕 Kortnee Marie 💕 • 28, married to my best friend, mommy to 2 handsome little men. TTC #3. Junior && Mason's mommy :)
I've heard that people get a positive opk right before they're supposed to get their periods, and turned out pregnant. I guess it could be an early indicator of pregnancy? ? I need opinions! Please comment!! Thank you in advance :)