Could Painful, Draining Boil On The Area Of Incision Near Breast Be Infected Stitch?

i have a boil under the crease of my breast for about 7 days, it began draining on its own today, redness around the boil and extending a bit to the sides, it is painful, it has not drained completely, i notice part of the boil is turning dark purple. should I seek medical attention, or is this normal. Also, this boil happened to develop on the same area I had incision from surgery aprox 3 years ago, could it be an infected stitch, which never desolved.