I would soak the snake daily. I've had balls that would need 2-4 soakings before they would let loose. Looking at the one picture, it appears the blockage is at the vent.
I can not see where it was fed to large of a mouse. I also do not see where an infection would cause this issue. I would soak the snake and turn the heat up to 95 degrees in it's cage. Keep a full water bowl, large enough for the snake to soak in if it wants to. Feel the underside of the snake and feel for lumps. Don't squeeze the snake, just run your hand somewhat tightly around the snake from the bottom side.
I do believe if it was a gastric issue, the bloating would be further up the body and not down towards the vent. The bloating appears to start in the stomach but it goes into the vent area. I do not see how any infection could be responsible for this.
How is the snake's attitude. Is it lathargic? Is it jumpy when you hold the snake?
Good Luck!
Jim Smith