What enlarges glands in the back of the neck?

Often infections: We have only few glands in the back of neck and swelling/lumps you feel are often from sebaceous cyst, which if infected can cause pain and may look like the one in picture here. Lymphnodes are typically small and mobile but can get larger and sore if there is infection near-by the area. If it is bothering you, get it checked. Boil can be lanced and you may need antibiotic. Consult doc. Good luck.