What do you mean you “failed.” Don’t believe anything the polygrapher tells you. They are liars who are paid to lie to your face for a living. If you really “failed,” you would have received official notification that your application is being discontinued and you would not have been invited back.
The reason you have had three sessions is because you are being interrogated over certain areas the government finds concerning, such as lifestyle and counterintelligence. The government cannot cram all of that into a 1-hour session, so they break it up over a number of sessions and they interrogate you in areas of concern. You have already been told twice that you “failed.” If you really failed, you would not have been brought back two more times. Again, they are just trying to get to you confess to something that a background check would not be able to reveal.
My advice for you moving forward is to not give up just yet. If you do not hear anything in the next few weeks, you can assume that your case is moving along in the process. Your recruiter would be the best point of contact to know where in the process your application is. They will be able to tell if and when your application is in adjudication, which is the final step in the process.