My betta has always had problems with constipation and has always gotten over it by fasting but today when I put him in cleaner water I noticed a very large lump on his belly/chin area. He couldn't possibly be pregnant because he's a male and I have no females in the tank with him. What is with this lump?

I would research either dropsy or a swim bladder problem. Its usually NOT a good sign and tends to lead to a dead betta. I hope he recovers for you. Maybe try feeding him skinned blanched pea meat.

Bred and owned all kinds of bettas.