If receding gums are present sensitivity will also be a problem. This means that where the gum is reciding, the dentine of the root is exposed and will be sensitive to even just cold air.
My suggestion would be to consult a dentist as soon as possible.
Another reason for a root canal treated tooth to be painful is, if the 'bite' is too high. This means that the tooth is taking alot of biting force and the ligament of the tooth gets painful (like a sprain).