Without knowing much more, it is hard to say. How long has the fish been there? Was he recently moved there from somewhere else? Is the water changed frequently? Is there any aquarium salt added to the tank he is in?
Regarding bettafix, it is good for attacking bacterial infections. That does not seem to be what your little guy has. I would guess he has swim bladder disease from being overfed and/or stressed, but even that disease usually causes a lot of belly-sliding on the bottom, which you did not mention.
If you can add 1 teaspoon of aquarium salt per 2.5 gallons of water to his current aquarium, and do it in a water change, not a staight salt add to his aquarium, he may improve. Betta Max may help, as it is s good anti-bacterial med.
I believe if you get a tank prepared at home (or bowl) with the right ratio of aquarium salt added, and have a stress-less transfer to your home, he can recover.
Here is a great post by Neenjar on salt baths ...