Hi, I Am 51, Am In Fairly Good Health With

Hi, I am 51, am in fairly good health with only medical history of significance, for 2 years ago. I believe I may have a spider bite on lower left breast because quite big red ring around what has grown to be an oblong lump about 1/2" long. A very small skin colored bump appeared about 3 weeks ago but in the last week it has gotten red hot and big lump. What could it be?