Ok just wondering if someone could give me advice. I've been taking ovulation test to determine when I ovulate my CD12…

Ok just wondering if someone could give me advice. I've been taking ovulation test to determine when I ovulate my CD12 test came back with a peak fertility. And my test remained positive through CD14. (I think I ovulate on CD14). Out of curiosity on CD15 I took another test which showed low fertility. Now on Cycle day 16 it's reading high fertility. I used the clear blue digital. This is all new to me and I have never reacted my days before just wondering if anyone out there has had a similar thing happen.