What Causes Purple And Blue Bruise On The Legs And Chest?

well three days ago i woke up with a small purple and blue bruising on my ribs and now my back is covered and my legs and chest its everytime i barley itch my skin it gets purple bruising! and i dont know if its from my lymphnods ive had three taken out on the right side of my neck and now a fourth one is back on the left side and its only been 6 months since the last one was taken out and no doctors or specalits can tell me why this keeps happening to me im only 19 and ive had this problem for alomost ten years help please!