I have a swollen tender purple lump node in the groin next to my testicle. it appeared a couple of days ago. no visible sore. otherwise healthy.

See below: The most common cause of a tender, purplish in color, lump in the groin area would be a furuncle or carbuncle which are a type of "boil". For small furuncles, warm compresses to promote drainage are usually sufficient treatment. For larger furuncles/carbuncle, incision and drainage by a physician may be needed with or without a course of antibiotics. Recommend MD evaluation for accurate diagnosis.