When a bracket is rebonded – whether because it has come off or because the orthodontist has decided during treatment to change where the bracket sits on the tooth – the tooth receives additional force from the new position of its bracket. This leads to increased discomfort. You may even feel pain in the neighbouring teeth, as the bracket in question is ‘pulling’ on them. The discomfort usually passes within 2–3 days and doesn't need painkillers or any other intervention.
This answer is for general information. Your own case needs an examination by an orthodontist.