I am having groin pain on lower left side with swelling. what could it be?

Possible Hernia: A hernia results from a weakening in the abdominal wall, allowing intestines to poke through. If you can "push" the swelling back but it returns, then it likely is a hernia. If the swelling gets worse, becomes reddened or is associated with increased pain/nausea/vomiting, you would need to go to the er immediately. The intestines can become trapped, stopping their blood flow (strangulation).