I apologize that no one has responded to your question sooner. Different experts come online at various times. I just logged on and saw your question. My name is ***** ***** I’m a biologist with a special interest in fish. I'm sorry to hear of this problem.
It appears that your fish has multiple problems. If he is over 2 years, this could be related to old age, and there may be nothing you can do about it. If he's younger than that, the first step is to test your water. If you find any nitrites or ammonia, let me know and I'll tell you what steps to take. If you don't have a test kit, most pet stores will test water for you if you bring in a sample in a clean glass jar.
If your water is fine and the fish is young, you can try treating. I would use a combination of two medications sold in pet stores - MelaFix and PimaFix. Just follow directions on the bottles. You can also add one teaspoon of aquarium salt per gallon of water. Don't use table salt - it sometimes has toxic additives. The three are safe to use together.
I know this isn't what you want to hear, but I believe you deserve honesty. Some of the symptoms your betta has may indicate a disease that can't be treated. The curved body is especially worrisome. It can be a sign of fish tuberculosis, which is usually fatal. All you can do is try the measures I told you about and see what happens. If you have more questions, just let me know. I hope your fish will be able to recover.
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