Pain months after root canal. Did an X-ray and it was short filled. Tooth is sensitive to hot cold and sweet. What to do?

Retreatment. Have the tooth retreated by a specialist.
Incomplete RCT. If the tooth had RCT, even if filled short, it's unlikely the tooth is sensitive to hot, cold and sweet. The source of that pain may be coming from another tooth. Having said that, you might have to have the RCT redone by a better qualified dentist. If none available you probably should have the tooth extracted if it hurts or there is an infection present.