I would be careful useing more than one medictaion at a time. If you use a medication too much, it is a possibility that your fish can become immune to the good effects of the medication.
I have heard the same for aquarium salts. Too many meds at one time can stress out the fish. Aslo, some very common meds, when used together, can be extremely flameable.
I would probably just use one med. Good job with the water changes! Alot of times, meds attack the symtoms but WC attack the problem. Reguardless, daily WC for your sick fish can be the best cure sometimes.
We can probably be able to diagnose for sure if you can put up some pics.
Hope Velvet gets better soon!