Is A Dermatologist Consultation Advisable For A Painful Lump On The Rib Cage?

In late October last year I saw a tiny red circular dot on my rib cage, didn't think much of it possibly was a mosquito or spider bite. In mid November the dot began growing under the skin to a pinky size dot, was somewhat hard under the skin. December is when it got reddish purple, was tender, and grew to dime size. Last week I was seen by my family doctor who prescribed an antiobiotic and I was to return for her to check it in two week. Just one week later (last week) I went back to her, it is now the slightly larger than a quarter and is very tender, painful even when I try to lay on it to sleep. I had an ultrasound last night and am waiting for results. The doctor wants me to have this surgically removed. Should I consult a dermatologist first? I'm taking Cephalexin antibiotic but it hasn't helped. Recommendations?