Odd issue with betta!

[Darkomot]

Hello, I woke up this morning and noticed that my betta was not swimming around as he normally would and that he was staying at the top of the tank and barely moving. I looked at him further and noticed something odd. He has an odd shape on the back half of him that seems to be sticking out on his sides. It almost looks as if he swallowed something angular? The weird shape is closer to his tail than his "belly". It is hard to capture this in a picture but I'll try my best. Does anyone know what this could be, and what I can do? I'm wondering if this is constipation. Thanks!
FYI: I am aware that most would not recommend keeping a betta with guppies, but so far I have had no issue doing so.

 

[itiwhetu]

How old is this fish, please

 

[matthew12098]

What are the water parameters and the size of the tank? Have you added anything new into the tank or fed your fish anything different?

 

[Darkomot]

@itiwhetu @matthew12098 My water parameters are: Ammonia: 0ppm, Nitrite: 0ppm, Nitrate: 20ppm, PH: Around 7.5. I also have the amount of aquarium salt in the tank at .7 tablespoons per gallon because I had a guppy with a bacterial infection that I believe was Columnaris. The tank is 10g and I just recently added 6 female guppies to the tank, two of them had to be euthanized because of some bacterial disease. The betta has shown no symptoms of a bacterial disease that I'm aware of. I feed my fish TetraMin Plus Tropical flakes and freeze-dried bloodworms occasionally. Does knowing all of this help? Thanks!!