Pos OPK after ovulation?

DH and I are TTC #2. I have PCOS so my DR put me on clomid, 50mg CD5-9. I started OPK's on CD11 and didn't get a + until CD18 and haven't gotten another since. According to fertilityfriend(and an apparent temp shift) I ovulated on CD17, one day before the + OPK. Has anyone else experienced this? I'm so confused.