Sometimes Last Week I Think I May Have Gotten A

Sometimes last week I think I may have gotten a bite of some kind on my lower left leg right above the ankle. I put Neosporin on it and it seemed to be okay. The area has itched. Now I see a pretty large slightly red circle around this area and when I press on the area it aches and even hurts, really feels like what a bruise feels like. What worries me is the Red circle. What could that be?