LH surge the day before period?

Elizabeth
I'm a day before my estimated period. I got a positive opk exactly 2 weeks ago. I've been taking an ovulation test every day, and after the positive, they've all been pretty faint. Today though, it was dark. Almost positive, but not quite. Is there an LH surge before the period? What might cause this? Thank you, and here's a picture of the test. It looks darker in person...