Pregnancy test went from positive to negative

I took 2 pregnancy tests today that came up positive as the dye went across and then the test line slowly faded. Has this ever happened to anyone? I'm almost wondering if it somehow picked up on my LH surge and then realized it wasn't the right hormone and it went away. I haven't had an LH surge yet this cycle, which is why I'm wondering that. I ran out of opks. I was supposed to get more in the mail by today, but they still haven't got here. When I took an opk yesterday, I still hadn't had my surge.