You would only be exempt from FICA tax (Social Security tax and Medicare tax) if you were a nonresident alien for tax purposes, and you are working legally in certain specific statuses, including F-1 or J-1 or certain diplomatic statuses. Nonresident aliens in other statuses, as well as all resident aliens regardless of status, are subject to FICA tax.
You said you were on OPT, which is F1 status. If you are still maintaining F1 status, e.g. if you are still on OPT and working completely within OPT guidelines and following OPT's restrictions, then (assuming you are still a nonresident alien, which for F1 usually means you are within the first 5 calendar years of being F1) you are still exempt from FICA tax. Otherwise, if you are no longer on F1 status, including if you used your non-OPT EAD to work which violates your F1 status (which sounds like what you are doing), then you are not exempt from FICA tax.