Late late late late !!!!!!!

It's been negative every single day since I've. Been able to test! (Also tested positive opk during my fertile window) !! 

What an earth is going on!? Has this happened to anyone?? 

I'm usually regular, usually have a CD of about 41 days. 

I've just been using all kinds of PG tests, good expensive brands and also the cheapie  ones. Do you think I can go for a blood test to check? Just so confused, haven't got no symptoms of AF of PG 🙃🙃🙃🤔 please please give me some advice because I'm just in utter confusion!