I have an enlarged lymph node in my neck just under my ear. i don't know any reason for this (don't have a sore throat or anything)?

Lymph node: Periauricular lymph nodes, near the ear, are normal. A lymph node that is smaller than a pea, nontender and slightly movable, is likely just doing its job. Lymph nodes help your body clear infections. A growing node, or associated fevers, should prompt you to see a doctor for a careful history and physical exam.

Enlarged Ln: You will need Ultrasound scan and possibly a USS guided lymph node biopsy. Nodes < 1 cm, freely mobile in the area and if they are solitary and non tender but soft may be normal. Usually painful Lns indicate reactive Lymph nodes. safest bet will be to get USS scan as mentioned and the get biopsy if USS is suspicious. Antibiotics trial may be helpful before embarking on invasive investigations.