Crown feels loose. Could it be gum swelling?

I would schedule an appointment with a dentist to evaluate the area asap.  This happens often with teeth with dated root canals and crowns.  There is a good chance that the tooth is breaking off in the crown and that is why it is loose.  If you leave this for too long the crown will come out with the tooth inside of the crown.  You are either looking at a new crown or an implant depending on what the diagnosis turns out to be.  Good luck. 

It sounds like you need to see a dentist to evaluate .  I suggest you get radiographs of the area and have it evaluated for possible infection