Polish nationality law says that a child born to a Polish parent is a Polish citizen at birth. It doesn't matter where the child was born. Even If only one parent is Polish and the child was born outside Poland, the child is Polish citizen. If a parent doesn't want the child to be a Polish citizen, Polish citizenship for the child can be disclaimed within 3 months of the child's birth.
If you father didn't do it then you are Polish citizen already. You just need a Polish passport and most importantly PESEL (same as SIN in US)
Your father didn't loose his Polish citizenship just because he became an US citizen.
Here is some info on how you can confirm your Polish citizenship: polishconsulateny.org
Confirmation of Polish citizenshipCitizens who do not have valid documents proving Polish citizenship (a Polish passport or ID) or whose personal data and citizenship cannot be ascertained, may apply for confirmation of Polish citizenship.
Citizens over 18 years old, who were born outside of Poland and/or have never possessed documents proving their Polish citizenship (a Polish passport or ID), prior to applying for the Polish passport at the Consulate must obtain a certificate confirming their Polish citizenship.
Certificate of confirmation of Polish citizenship or its loss, or refusal of its confirmation, is issued by a Provincial Governor (Wojewoda). Applicants residing abroad submit an application through the Consulate according to their place of residence. After verification, the application is transferred by the Consulate to the Provincial Governor Office, in accord with the applicant's last place of residence in Poland (in case of the applicants who have never resided in Poland - to the Provincial Governor Office in Warsaw). The decision of the Wojewoda is forwarded to the applicant through the the person residing in Poland authorized by an applicant for the service of correspondence.. from the Provincial Governor's Office.