Usually, the Mitzva of Pidyon Ben is not carried out for the first-born son of a bas-Cohen, a daughter of a Cohen, or the first-born son of a bas-Levi, daughter of a Levite. In your case, however, due to your having had relations with a non-Jew, your status changes to chalala, and thus your son will need to have the Pidyon Ben.
This should be accepted with understanding and joy, for there is nothing more dear to HaShem than a baalas teshuva—a returnee, who has come back to her Father in Heaven. This is especially so when we take into consideration the fact that the whole generation may be considered as though their sins were committed by accident, because they have the status of someone ‘captured by (the outlook of) the secular world.’