Hi NuocCam, I'm sorry your betta has dropsy. :(
Could you fill this in so we can help you better: http://www.bettafish.com/showthread.php?t=49233
First thing i would like to tell you is stop putting melafix in the water, it is very bad for bettas.
This is from the emergencies sticky:
Do 100% water changes everyday. Increase the temperature to 84*F.
Add 1-2 tsp/gal Epsom Salt. Use API General Cure OR API Erythromycin OR Maracyn II and/or Maracyn for best results. Feed something containing Metronidazole, for example, Jungle’s Anti-Parasite pellets. If caught early, Dropsy is curable.
This is what is suggested by Darkmoon, our resident doctor. :) I hope it helps you!