I urge you to cancel the melafix treatment for the time being, while it does indeed have healing benefits for many fish it is unfortunately detrimental to betta fish because it can coat their labrynth organ and make it difficult to breathe. betta fix is actually just a more diluted version of melafic and has less of the key extract that causes the concerns.
Now as to his spot, can you get us a picture from above? perhaps at feeding time.
I can clearly see the spot in the picture but I am unsure on a few things which can help diagnose= is the spot fluffy or slimy? Raised or flat? Are there scales under/over the spot or does it look raw?
Another question is about his actions, have you seen him rubbing/hitting/flashing against anything that might indicate the spot is itchy?
Now as to his spot, can you get us a picture from above? perhaps at feeding time.
I can clearly see the spot in the picture but I am unsure on a few things which can help diagnose= is the spot fluffy or slimy? Raised or flat? Are there scales under/over the spot or does it look raw?
Another question is about his actions, have you seen him rubbing/hitting/flashing against anything that might indicate the spot is itchy?