Are OPKs really that reliable?

Are they? I have egg white CM, cramping, and my sex drive is through the roof. But these opks aren't getting darker. Are they that reliable? They should be getting darker right? I took one yesterday it was lighter than the control line now I take it this afternoon both lines are way lighter. It's so annoying. I had lab work testing if I am ovulating and it confirmed I do ovulate. So wtf? Thanks