the fact that it is coming and going is the boas own immune system, trying to fight it off periodically when the white blood cell (immune cells) gain momentum, probably triggered when the snake is not on the cooler side of the cage. it is better to take it to a vet and have a culture and sensitivity of the nose, mouth, and inside the mouth done, and sent to the lab for a pathologist to look at and run a full culture (which tells you what, if any, organisms grow, and sensitivity is what the organism(s) that are grown are either resistant to or sensitive too, (regarding which antibiotics or anti-fungal medication need to be used to fight the organsim)