My 2 Year Old Son Has Hickey Like Marks On

My 2 year old son has hickey like marks on his neck. One on each side. He had one about a month ago as well when he was sick. I noticed it at the doctors office when they took his temp. He tested pos for RSV at that appt. I asked the doctor what the place might be he said may just be a rash and to keep an eye on it and it went away as he started to get better but now they are back. Any idea what it could be and should I take him back to the doctor?