If what you said is true, the first and foremost question you need to decide is what you want to do. You can get an injunction. You can also get monetary damage. Unfortunately, in terms of fair use, there are certain factors against you. First, you posted them on a public forum for free. It is hard to see whether or not you have a commercial purpose in mind, such as publishing those articles commercially later. Second, you did not register them in the copyright office, which does not mean you do not have copyright protection but you cannot get statutory damage. Third, it would be hard to prove the commerical purpose of the other websites or newspapers. Finally, it is hard to prove your monetary damage.
You need to sit down with a copyright attorney to figure out whether the other use is fair and whether you have an infringement case against the others. It is possible, though, to send a cease and desist letter to the others to prevent such use in the future.