It is possible that the symptoms have not improved after four days of treatment with Cefadroxil, as this is the expected outcome in most cases. I recommend that you wait another 24-48 hours before consulting a doctor again. Additionally, I suggest that you trace the area around the sore/reddened area with a pen to better assess the evolution of your symptoms. This will help the doctor to better understand your condition. It is also possible that the lack of improvement could indicate that it is not an infection at all.