What could of happened :(

[AlyssaJulianna]

Well, today was the day my first Betta died.
I fed him well, kept his tank clean, and taught him a trick.
When i woke up this morning he was on his side.
i picked him out of the tank to examine him.
hes a blue betta,and his stomach was so puffed up what it was white,
and he had a very large bump right under his mouth. ITS SO ODD, JUST YESTERDAY HE WAS SWIMMING CAREFREE.

Housing
What size is your tank? Gallon
What temperature is your tank? Room Temp
Does your tank have a filter? No
Does your tank have an air stone or other type of aeration? No
Is your tank heated? No
What tank mates does your betta fish live with? None

Food
What type of food do you feed your betta fish? FLakes, Pellets, Blood worms
How often do you feed your betta fish? Everyday, in variation

Maintenance
How often do you perform a water change? Once a month
What percentage of the water do you change when you perform a water change? All
What type of additives do you add to the water when you perform a water change? Betta safe water conditioner

Water Parameters:
Have you tested your water? If so, what are the following parameters?

Ammonia: -
Nitrite: -
Nitrate: -
pH: -
Hardness: -
Alkalinity: -

Symptoms and Treatment
How has your betta fish's appearance changed? Large bump on mouth, huge tummy
How has your betta fish's behavior changed? no
When did you start noticing the symptoms? 3 days ago
Have you started treating your fish? If so, how? fasting
Does your fish have any history of being ill? yes
How old is your fish (approximately)? year and half

[Sakura8]

Hi AlyssaJulianna and welcome to the forum. I'm so sorry to hear you lost your betta, losing your first betta is always so hard. :( I'll ask a few questions because if we can find out what caused this we can help you prevent it the next time you get a betta.
What size was his tank and how often did you change the water?
Did you use a water conditioner to treat his water?
Did he have a heater?
And do you know if his stomach was bloated up before he died?