If it ruptured puss it is not lympohsis.
If it is hith it is easy to treat. You can have perfect water and sometimes get it. Heximita is the protozoa that is demonized as the cause in cases like yours. Some times just the stress of moving can let this bug flourish.
Metronidazole works very well and it is cheap. SeaChem sells a powdered form that is my favorite to use.