Swollen lymph in groin?

Probably syphilis: An open, painless genital sore (chancre) plus lymph node swelling in the groin usually is primary syphilis, probably acquired 2-3 weeks before the sore appeared. Penile cancer is much less likely but could do this, as well as certain non-STD infections. All possibilities are dangerous. See a doctor or clinic ASAP; you need diagnostic testing and probably an injection of long-acting penicillin.