I noticed my breast is bigger, painful and swelling on one side. What should I do? I tried expressing the milk but there seems to be no milk already but i still feel very painful. The bigger breast has more milk supply compared to the other one.

I could be wrong, but it sounds like engorgement, to a point where your milk won't come out. It might be uncomfortable but nursing frequently, with no more than 2 to 3 hours between feedings, helps. You can also try manually expressing the milk while in a warm shower. To soothe the discomfort, you can soothe the pain and help relieve swelling by applying cold packs to your breasts for about ten minutes before or after nursing.