No test line on my opk?


so I'm cycle day 14 and should be ovulating around this time. but I took an opk and there is no test line at all. which is very weird because I've always gotten some kind of line even if it's faint. I just started using a new brand of Opks I got on Amazon called Clinical guard and none of them have shown an lh surge. I was using Opks by the brand proven and they seemed to work just fine always had some kind of line. do you girls think it's the brand or I just don't have enough lh in my system?