What is this knot under my chin?

There is this knot under my chin on the inside of my skin. I don't know what it is. I had it before about a month ago for about 3 weeks. I went to the hospital because my tonsils were severily swollen and had to be removed. A week after the surgery, I had to go back because of a blood clot and had the procedure done again. After this second surgery, I noticed the knot under my chin was gone. Two weeks later, I went and worked out and the knot under my chin is back. It is a little bigger than the size of a pea and it doesn't really hurt. The ear, nose, and throat doctor didn't know what it was, but he seemed really concerned about it. It's just worrying me. Any thoughts would be appreciated, thanks!