You mentioned you changed the filter bag - Did you dispose of everything in the filter area and replace it? If so you have thrown away the Beneficial Bacteria to keep your tank cycled. Filter media needs to only be rinsed in used tank water and put right back in. Unless it is completely falling apart only replace half at a time. This way Beneficial Bacteria will not be thrown away.

Is there a reason why you are using both Prime and Nutrafin Cycle? Frogs absorb everything through their skin, so less is always better. Prime alone (2 drops per gallon) added to fresh water before adding fresh water to tank. Weekly water changes should be 50%. I would do a good 50-60% today and use Prime only. Weekly 50% water changes along with gravel vac will keep the pH more stable, replenish minerals in the water, remove nitrates etc.. Make sure the new water pH is close to the same pH as the tank and same temperature. If the pH is way off just add the water back slowly over the course of an hour or so to acclimate them and not shock them.

Could your frog have gotten his foot stuck under an ornament? Another issue could be the betta - The betta could have bitten the frogs foot thinking it was food. Bettas have teeth so this could easily happen.

Female ADF's tend to be much better hunters than the males when looking for food. If pellets aren't soaked first prior to feeding and she eats to many to fast she can also get gas which in turn will cause her to float. Are you able to see through her belly (left side) with a flashlight? If you can and it looks like you can see right through her it could possibly be gas.
I have a photo here of one of my frogs a couple of years ago that had gas: http://jancy.flippersnfins.yuku.com/album/view/aid/122762#.UIp19bSdL8s]

I would keep the frog isolated, keep his water as pristine as possible and using only Prime for water conditioner. Safe Meds for ADF's: Click here If you think it's a fungus I would try these but try it at half the dosage but for the correct amount of time and only treat the frog that's ill. I've never had to treat mine before so I would follow the directions but only change to 1/2 dose.