Slow day in the park. Lactate threshold?

I'm back to my regular pace huffing and puffing to maintain 15.5-16.5 mph up the hills in PP. I dunno what's happened? I have a feeling it has something to do with the way I've been training, maybe pushing it too hard too often, riding too near my lactate threshold all the time. Some folks from the Kissena club group suggested I read this, looks like a good recommendation.