After washing my face at night, I wait 20 minutes before applying my Tretinoin Gel, then I wait another 30 minutes to apply a moisturizer. Some of the gel sheds off when I apply the moisturizer. At first I thought it was my skin flaking, but realized that it was elastic and seems to be the gel rolling up and shedding. I don't want the gel to be ineffective; I even tried waiting an hour, but the same thing occurs. Is this normal with Tretinoin gel?