What causes lymph nodes to swell around the neck,armpit and back of the head at the same time?

Lymph nodes: Swelling of lymph nodes is common from viral processes, bacterial infection or tumor. Regional lymphandenopathy would likely be associated with infection, however, breast cancer in a woman could cause this or lymphoma.

Lymphadenopathy: You don't mention your age. If you're young I would think of infectious mononucleosis or leukemia. If you're older, lymphoma or leukemia would be high on the list of causes.