Try to get a follow up x-ray from your dentist. The best way to confirm the root canal treatment failure is by an intra oral photography as sometimes symptoms is only suggestive but not conclusive.
A root canal treatment which has failed usually will have to undergo re-treatment, extraction or endodontic surgery depending on case requirements.
It is always wise to maintain close communication with your dentist to identify and recognize the symptoms of a failed root canal treatment. As your dentist has been keeping your records and developments after the treatment, identification of a failure could be a breeze. If symptoms persist, don’t be alarmed but make an appointment to consult your dentist