I live in Kansas. Friday I was cleaning inside a shed full of dried leaves and wood. I felt a sting in the inside of my arm (elbow). It looked like a mosquito bite. Now (Tuesday) it is black and blue-purple about the size of 3 quarters. Following a white-gray ring around that. Then a red swollen around that. Extremely sensitive to touch or even lightly blowing on it it painful. Red hot itchy rashes spreading over my body and low fever. There is a large hard knot where the center (black-purple area) should I be concerned about the knot - what is it"