Since I couldn't wait for another 4 or 5 days, I went to the Emergency at our local hospital today, and an assistant physician had it checked. I told him it was there for three weeks and I went there only because of its irregular shape, big size and painlessness. He looked into it and felt underneath it and then checked the other parts of the inside of my mouth, said it was only canker sore. And although I did not mention it, he assured me that it was not cancer. He prescribed me some magic mouthwash and Motrins, and told me to schedule a follow up it doesn't get better in four days. So guess I could relieve and cancel my appointment with the oral surgeon now. Thank you everybody for your responses and support!