I use Eucerin's SPF 30 for my face in the day and Tretinoin at night (prescribed by my doctor). The Eucerin leaves a white residue on my face no matter how much I put on, and I want to use the proper amount to protect my face. Is there a moisturizer I can use under the Eucerin that may make the sunscreen easier to apply? I don't want to stop using it; I have cystic acne and don't want to make it worse. Thank you in advance.