I Noticed A Knot On My Left Leg A Little

I noticed a knot on my left leg a little over a month ago, I went to my doctor two ago with concerns about it, but he payed no attention to it, since then it has gotten a little bigger and the knot is light red in color and is very sore causing my leg to hurt and ache. What could this be? Should I go to the er and have it checked out?