Betta Fish: What is this bump on my betta’s fin?

I’m so worried about this bump that has appeared on his top fin all of a sudden. I’ve been looking online and I can’t find much answers or anything similar to what he’s going through. Is it a tumor or something else? The past few days I’ve had him in a hospital tank. He’s eating but has trouble swimming. When he’s about to rest that bump seems to drag him to the side. That’s what’s really scaring me. I’ve had him for a little over a year. 2nd photo was a month ago. 3rd was a few months back when he was perfectly healthy. I don’t want to think the worst 😭

Tank size: 5 gallon
Temp: 75-80F
Filter: yes
Heater: no because where I live it’s warm anyway
Nitrate: 10 mg/L
Nitrite: 0
pH: 7.2
Ammonia: 0
GH: 100

He has a few small trumpet snails and neocaridina shrimp as tank mates. Nothing sharp in his main tank, a bunch of live plants and hides. Water changes weekly sometimes twice a week.