If I understand you correctly, you have already filed the I-485 and it has been received by the USCIS. Thus your status is no longer F1, but you're now an I-485 adjustee. Note also that filing an I-485 is an express declaration of intent to immigrate, and an F1 is issued contingent upon your lack of intention to immigrate, so the F1 really can't survive that declaration. It thus appears that you need to apply for EAD under your I-485 rather than trying to seek OPT under your (former) F1 status.
Your college may have an academic advisor you can instruct you more specifically about the immigration issues in your case.

