Swollen lymph nodes in groin for a litttle over a month, doctor said its just infection antibotics made them smaller but not go away. is this cancer?

Not cancer: Usually there is no need to treat these. The nodes are just preventing keeping bacteria under control. Everybody has some in their groin on each side. When i used to get barefoot in the summer, mine would get quite prominent. If they shrank on antibiotic rx, they're almost certainly benign. Malignant ones will either be one-sided or all around your body; hard, stuck to things, or make you feel bad.