A dermatologist prescribed Hydroquinone 4% for me one week ago. Since then, I have noticed redness and tightness at the sites. I have also noticed a very fine rash. My dermatologist said this was to be expected and did not seem too concerned. My face hurts! How much longer should I continue to use this product, if any? I have been using it as prescribed, twice daily, as well as using sunscreen when outdoors.