Crowns post RCT are necessary , as due to no blood supply , the root canal treated teeth are brittle as compared to other vital teeth. Due to their brittle nature they can break under stress e.g. eating hard foodstuffs or habits like pencil biting etc. A crown protects the root canal treated tooth from all such masticatory forces that may otherwise cause the tooth to crack or break. In your case it makes sense to wait until your pain subsides. Go for crown only after all your symptoms go away.

Root canal treatment is a procedure for infection control and crowns are given for giving strength to otherwise weakened tooth structure. Please inform your dentist about the persistence of symptoms and you can wait for a few days till they subside. Requirement of a cap is best judged by the dentist who has examined the case clinically. Regards