My 2 year old mutt was napping on the floor tonight on his back and I was brushing him when I felt a bump under the skin on the inside of his back leg/groin area. It's probably where a lymph node would be. The other side didn't have this swelling. It's not visible, I had to feel around to find it. He just got his Parvo/Bordatella shots today so maybe his lymph node is swollen because of that? It's probably nothing but he's my first dog and I'm a hypochondriac!