ovulation test help

I tried searching old threads but I'm not really getting the answers in looking for. New to this OPK and first month TTC
Question is: this is my 4th fertility day according to glow. However i took a clear blue advanced and it was a big negative. Not even showing some fertility. I'm confused because I thought that test told  you 4 fertile days. Saturday is my last day according to glow. Help please!!