Could a lymph node behind ear be cancerous it feels hard when touched, i haven't got infection am feeling fine other than i have high prolactin levels?

Any hard: Lymph node needs to be evaluated. Cancer can occur, but is not likely. Ask you doctor to evaluate it for you.

It depends....: Enlarged nodes can be cancerous especially if they are painless and hard to feel. But a lot depends on the size of the lymph node. If it is more than 1cm (half inch) and it increases in size over the next month or two then you need to get a medical exam to make sure it is not cancerous.A biopsy of the node is the best way to find out what is causing it to enlarge.