The vast number of people on this MedHelp system have similar problems where the tinniest little thing is made out to be their death and one reason I hate responding to anyone. The slightest slip of the tongue can send that person to the hospital screaming they were told their world is coming to an end when in reality they were told they probably should have someone pull that sliver out of their finger.
That said, you probably should have a dentist take a look. Go from one dentist to another telling them the problem and that you have no money. You may find one that'll help you out in one way or another. Next, What about Medicaid? Being a US legal citizen you can get medicaid and that covers dental care. (so I'm told).
To relate a similar story; I had a bad tooth ache and have been told all my life that dentists are far too expensive to go to without insurance to pay for them. The tooth pain got so bad I had no choice. After an exame, dental x-rays, pulling a tooth, and ect... The total bill was $100.00 and I was expecting $5,000.00. So, ask the dentist how much he will charge for his services.
As long as the root canal was sealed, you should be all right. Did the dentist finish the job, and the next step was a post and core and crown? The last one third of the canal is sealed in a root canal, and then a temporary filling or permanent filling goes into the lower part of the canal. If that has fallen out, then the canal could be filled with food debris and could cause decay and irritate the gums.