I Am 35 Years Old. Have Not Breastfed For 2

I am 35 years old. have not breastfed for 2 years. I woke up yesterday with severe left breast pain and tenderness. it is red, warm, and painful (burning and sharp both). today i can feel it a bit better still very sore but feels like a long firm inflamed milk duct about an inch by half inch right above my nipple. i have general malaise today and a fever of 100.5. I am wondering if this is an infection or potentially cancer?