An attorney would need more information to determine if you have a valid claim or not--(1) what type of illegal activity did you report? (2) what was in the journal that they claimed was the basis for your termination?
There are federal whistle blower laws that protect employees who provide information of illegal activities which result in fraud upon the U.S. government. Most states have similar laws. And there are several federal laws which prohibit retaliation for opposing various acts of unlawful discrimination. You may fall under one of these safe harbors but would need to provide more information to an employment lawyer for a solid answer.
Employment-related cases are very complex and fact-dependent. As others suggested, you should contact an attorney with experience with employment matters in your area. Most such attorneys will offer a free consultation, either over the phone, or in-person.
Public responses provided herein are for informational purposes only and are not intended to, nor do they create, an attorney-client relationship or privilege.