You will NOT derail any of your efforts at good health or weight loss because you can't exercise for a few days. Take care of yourself first. Give your body time to get over this sinus infection. Can you exercise ? Sure and you've seen what happens. You feel worse !! take a few days to get over this cold/flu. get some rest. push those fluids. lay off any exercise.
The fact is, doing more exercise will not speed up your weight loss. You didn't gain the weight overnight. it's not coming off overnight. So, don't beat yourself up because you haven't seen a change in the scale in the last three weeks. That really is perfectly normal. Right now, your body may be retaining fluid because of the sinus infection. Once you get better, your body will release that excess fluid. You'll probably see a loss on the scale in a few days.
But you have to be patient with your body and yourself !!! Remember, weight loss is a slow steady process that takes time.