There is infection in tooth.visit dentist get x ray done. If there is infection in rc t treated tooth you may need to do re root canal treatment. But there may be other carious tooth which may be cause of pain and swelling.

Get an IOPA Xray done of that tooth and visit dentist. Start having, 1) T. Augmentin DUO 625, 3 times/day, total 10 tablets. 2) T. Metrogyl 400, 3 times/day,10 tablets. 3) T. Parasafe 650, only in case of mild pain, maximum 4 times/day. If doesn't relieve, T.Ketorol DT,  one tablet at a time, maximum 3 tablets per day, only if moderate to severe pain, dilute in water and consume. 1,2,3 to be consumed after food. 1 and 2 both tablets to be consumed(all 10 tablets to be strickly consumed) as per instruction even if pain subsides after a few tablets. If no pain, do not take any of no. 3 medicines. 4)C.pan D, once a day, before food for 5 days. 5) T.chymoral forte, 3 times/day for 2 days. Total 6 tablets. Before food if no acidity problem.otherwise after food.