Originally Posted by callistra
It's also possible he has a tumor or general organ failure not related to infection.. but if it is bacterial kanaplex should help.
I was about to say, our girl has a bump kind of like that, so I did a lot of research, bettas can have tumors (liquid or solid), boils, cysts, and abscesses. For the most part, they're very unsightly, and draining is not recommended unless it begins to severely affect the quality of your fish's life.
The procedures for treating bacterial or parasitic lumps won't affect these the same way.
The thing that's bothering me is that he's not pooping, that's the only major difference between my sick fish and yours, Jade is still pretty regular.
We're hoping your guy feels better soon.