Beta Help!!

[Cole Harlow]

Hi a few weeks ago my betta has became very bloated and always floated to the top. I figured out it was a common problem for betta to become constipated so I fasted my fish and fed it pees. Over the next week or so my fishes bloating decreased until it was back to its normal size. Despite that it has returned to it's normal size my betta still continued to float to the top and is very lethargic despite all my efforts. I'm. Addition today I noticed the bettask fin's were beginning to rot away. I have been keeping up on water changes and the temperature is at 80 to keep the fishes metabolism up. Any suggestions on how I can help my fish or if it is hopeless.
Thank you