Hi - My Name Is Lizanne Hayes. 55 Yo Female.

Hi - My name is Lizanne Hayes. 55 yo female. Developed a large boil overnight last weekend - It was located under my armpit and grew from a small pimple on Friday to a huge mass 10cm by Monday. It was so painful I couldn't sleep or put my arm down. I had it lanced on Tuesday by a dermatologist but after drainage she said there was still a large hard mass in the area that she couldn't remove. It is just as sore as the boil and a mass. What could this be?