Enlarged, painful breasts. Should I lose weight or just go to plastic surgeon for reduction?

First... First have your doctor evaluate you to make sure you are ok. Then lose weight to a weight you can maintain long term. At that point, seek a good plastic surgeon if you don't like the way things look . :).
Mammogram first. Depending on your age, you should visit your doctor and have a thorough physical exam. This may include a mammogram to make sure there aren't any cancerous growths.