5days of +opk

*D*
I had 5 days of very positive opks. On the fifth day I tested around 2pm and it was very positive. The test line was darker than the control. Then at about 9 pm tested again and absolutely no test line at all. How can that happen so fast? Today it is still the same with a negative opk but I got sick after eating. I'm only 4dpo btw.