The people on this forum do want to help you with this issue, how ever in order to do so, additional information will be needed. If you could please answer the following Questions you will assist the experts here in being able to try to help you and your Betta.
What size is your tank?
What are the water parameters = ammonia, PH, nitrite, nitrate?
Are there any other fish, snails, shrimp ect in the tank?
How often do you do water changes?
How much of the water do you change?
Do you use a water conditioner?
Do you have a heater in the tank?
What is the temperature of the water?
Do you have a filter on the tank?
What foods are you feeding,how much and how often?