My Betta is Bloated????

Help! I bought a Betta about a month ago, he seemed to be doing fine until I started to notice that he was bloated?! I fed him 2-3 pellets every day but when I saw he was "bloated" I didn't feed him for three days and then fed him a pea. He still isn't getting better. He's worse now! Please help!

This is a picture from when he started to become lethargic. His belly is more swollen now.
Update: He is having difficulty swimming and is always laying on leaves or the sand.

 

Can you tell us more about his environment? Like what size, temperature, parameters. What kind of food do you give him? Is he pooping?

 

Can you tell us more about his environment? Like what size, temperature, parameters. What kind of food do you give him? Is he pooping?

He lives in a 5 gallon filtered tank. The substrate is sand and there is one live plant with some decor. The temp. is at 78f. I feed him baby Betta micro pellets since he won't eat normal sized pellets. I have not seen him poop since the day I got him.
I took another picture of him, he seems to be losing color.

 

That's a good size! Do you know what your ammonia, nitrite and nitrate levels are? If you don't have a test kit can you please get your water tested at the pet store? Take samples of both tap and tank!

 

That's a good size! Do you know what your ammonia, nitrite and nitrate levels are? If you don't have a test kit can you please get your water tested at the pet store? Take samples of both tap and tank!

I only have an Ammonia test kit and I tested the water in the tank with it, it came out at .25 ,the chart says its safe. I'm sorry I don't know what the nitrite or nitrate levels are. I can't go to the pet store today, but I would be really thankful if you could help me with the information I have given so far.

 

Without knowing what the parameters are I can only guess at what the problem could be. Until you can get those, my recommendation is to do a 50% water change and put enough dechlorinater in to treat the whole 5 gallons. What kind of dechlorinater do you have?