What Do Puss Filled Sores On Head Indicate?

I am a female, 25, and I have sores at the back of my head and they hurt. Usually they would ooze puss or blood and then would dry up. However, when I wash my hair the scabs come off and then they become tender and ooze again. It has now spread to the top portion of my head. It leaves bald spots and my hair has stop growing. I feel uncomfortable. What is wrong with me? Can this be a symptom of Cellulitis. I have the same problem on my legs with sores oozing puss and blood.