Mobile tooth after root canal with pain is a sign of periapical abscess/cyst/granuloma

If you just got root canal treatment without a permanent filling or crown, there are chances of reinfection. If you got the crown too, see your dentist.  It might be referred pain from another tooth. But there are also chances of reinfection or missed canals which were not filled. A clinical examination and radiograph would be necessary for a confirmed diagnosis

Don't worry about shaking of your tooth... You get an x-ray and repeat your root canal treatment and fix a cap before it gets late... Or else your tooth can break ... There can be another possibility that your teeth may have slightly broken or cracked so whatever the situation can only be known by an X-ray ...

Photograph of the tooth and xray needed to know whether the pain is due to teeth problem or gum problem. In your case if the tooth is mobile then you might have periodontal problem due to Gums and boneloss.

iopa xray of that particular tooth is needed to know the present condition of RCT treated tooth and it's surrounding bone.apart from that clinical evaluation is also mandatory.