What Does A Painful Knot In The Middle Of The Neck Indicate?

For almost a year I ve had a painful knot on the back middle part of my neck. I went to the doctor and they diagnosed it as Folliculitis but after taking the antibiotics there was progress. I returned to the doctor because another knot appeared. They then diagnosed it as a sebaceous cyst and prescribed some ibuprofen. The pain became so unbearable that i went to another doctor and there was still no change. I now have three of these large knots and my vision is becoming blurred.