You can try bettafix and water changes. how often do you do it? It certainly sounds like fin rot.
I highly recommend the salt bath though, it is not as difficult as it seems. Let me give you the "easy" method to be sure you have the right amount of salt.
1) go to grocery store and buy a gallon of water, drink it all or water some plants.
2) fill the 1 gallon jug with tap water and dechlorinate it.
3) put 1 tsp aquarium salt into a shot glass, poor some of the treated gallon into it.
4) microwave the shot glass of water and salt for a minute, remove and stir, then add 30 seconds time as needed until the salt is dissolved
5) poor the shot glass contents back into the gallon and shake the gallon to mix it
6) poor from the gallon into whatever you treat the fish in.
7) follow the steps form my how to form the point of adding the fish to the water.
I have been keeping fish over 25 years now and have always found this to me the most effective treatment.
add betta fix to his freshly water changed tank water as a preventive\healing boost.
The best solution for fin rot I have found is to stay current on water changes and it usually does not show up at all ;)