First and foremost, you should take care of yourself! Sounds like you need plenty of rest and fluids. I'm a mom so I get to say these things ;-)

As to writing or plotting, that's a tough call. Of course, my advice is to write as you plot, the worse being that you might take a wrong turn but that's okay - put it aside to edit another day - never delete anything written for a first draft. Who knows? Maybe you'll like it after all. Or not - that's what red pens are for...

I hope that you're feeling better soon!