Swollen inner thigh, not lymph node, with red blotch, no itch or pain, 2 inches down from a 2 day old tattoo. What could have caused it?

Many possibilities. If it's warm to touch and the redness is spreading it's possible it could be cellulitis (a skin infection). If this doesn't improve, and certainly if it worsens, you should have this examined by a physician. If it is cellulitis, you will need to have antibiotics Rx.