What Is The Perfectly Round Red Circle On My Neck?

I have a perfectly round red circle on my neck; however, it doesn't itch or burn. I would be hard pressed to know it was there, if I couldn't see it in the mirror. Do you have any suggestions?? I go to the doctor tomorrow for blood work, so he should be able to see it then. For now, I just wonder if you could help in some shape, form, or fashion. Thank you for your time and consideration on this matter.