My dr removed and replaced loose bracket. i felt so much pressure and pain. dr said it's normal to feel pain coz teeth are still moving. is that true?

Yes, it's true: The bone is sore due to the action of the braces and wires. You should be fine.

Possible: What he told you is true. There is a posss that there is something happening if there is a filling in the tooth. Residual caries(decay) is a condition that exists under a restoration. It many time does not show itself on the radiograph. If the discomfort does not subside see your general dentist. The contact of chewing may also have the tooth a little "Wiigged Out". The bite can be adjusted.

Should subside: Within a day or so. The pressure is common and to be expected. However if it lasts more than 2 days, call your orthodontist and discuss with them.