There isn't much worse than a sick tiny baby. All you can do is attempt to comfort, and hope for the best. My little Canonball fell victim to what our pediatrician suspected was RSV.
Canon was really struggling to nurse those first few months. When he got sick something switched and he actually started rejecting binkies and bottles. While I was pretty bummed that the binkie got kicked to the curb, I was more than happy that such an unpleasant thing turned out to be a blessing to me. I love nursing my babies (and I didn't mind not having to pump 5 times a day either)!