If your faith is in an institution or organization, it should be shaken. If it is in Christ alone, it cannot be shaken. But really, why would the virginity or lack thereof (after Christ's birth)of Mary shake your faith. The miracle was the Incarnation and the virgin birth and those are not brought into question.
So, let me ask you directly: Do you believe that to contracept is to sin?
Secondly, do you belong to a church which teaches it is a sin to use artificial birth control?