Is this a bite? (with photo)

About three weeks ago I had a red rash on my ankle, about an inch across. A nurse practitioner thought it was "a bite of some kind." It itched for a day, did not grow, then faded completely in about a week. So apparently not lyme. Today I had another, almost identical rash on the other ankle. Here's a photo: The only time I am not in shoes and socks is when sleeping, usually under covers but not always. I haven't noticed anything in the bedding. So two very similar rashes three weeks apart. Any ideas? A single bed bug, a reaction to a flying insect bite, something else?