Started penicillin wed. thurs night vaginal itching. painful invisible lump right labia fri night. subsided next morning. now, just severe itching. ?

Lots of things: May be unrelated. Antibiotics can lead to a vaginal yeast infection. Should not cause the bump. May be worthwhile to have a quick exam.

You may: Have a yeast infection from the antibiotics. If the lump at 700 or 400 it may be a bartholins abscess which can improve (if caught early) w/ antibiotics. Try a Monistat suppository. Good luck.