Hi, can you post a photo of him?
Do you have any Epsom salt in the house? It should be 100% magnesium sulfate. (No dyes, additives or perfumes.) If you don't have any, you can get it at supermarkets or pharmacies (Walmart, CVS, etc). Petstores won't have it.
How large is his tank? Based on what you've told us, I'm pretty sure you'll need to add Epsom salt to his tank, in order to help his swim buoyancy issues. Start with a dosage of about 0.50 teaspoons Epsom salt per gallon of water. The easiest way to do this is to put some of his tank water in a cup. Add the correct amount of Epsom salt. Stir until the salt is completely dissolved. Then, slowly pour it back into his tank over the course of about 30 minutes.
Also, please fill out the form so that we have more information. Answer as many of the following questions as you can. Put N/A beside anything you cannot answer.
What size is your tank?
What temperature is your tank?
Does your tank have a filter?
Does your tank have an air stone or other type of aeration?
Is your tank heated?
What tank mates does your betta fish live with?
What type of food do you feed your betta fish?
How often do you feed your betta fish?
How often do you perform a water change?
What percentage of the water do you change when you perform a water change?
What type of additives do you add to the water when you perform a water change?
Have you tested your water? If so, what are the following parameters?
Symptoms and Treatment
How has your betta fish's appearance changed?
How has your betta fish's behavior changed?
When did you start noticing the symptoms?
Have you started treating your fish? If so, how?
Does your fish have any history of being ill?
How old is your fish (approximately)?