Hello morioh, 

It sounds like the multiple doctors you have seen are not concerned about it which is reassuring. Unfortunately no one here will be able to tell you what this is but I hope that you will hear from the experience of others on the forum who have been in a similar situation and that they will come and share their story with you. You could if you are really worried try and get yet another opinion and ask whether they think it would be beneficial for you to be referred. There is information on this page on getting a second opinion. 

Best wishes, 

Lucie, Cancer Chat Moderator