Suddenly I'm not getting +opks?

For the past 2 months I have not gotten a +opk. The second line doesn't get dark at all and sometimes it's stark white except for the control line. I've gotten +opks every month and can even feel when I ovulate except these past 2 months. I go to my doctor soon but I'm wondering if any of you ladies have any ideas to what could cause this. My cycles are still regular too