Round 3 of clomid

Laney
Looking for advice this is my 3rd round on clomid CD 5-9. The first round I got a positive on the OPK on CD 14 and the second round I got my positive on CD 13. What I'm questioning is my cycle length is 39 days and according to this app I would ovulate around day 21. Am I getting false positives on the OPK?