Under my chin on the upper right of my neck is a hard pea sized lump. What could this be?

Lymph node or cyst. A small lump in the neck is usually a 'reactive lymph node' as the result of some viral upper respiratory infection. Lymph nodes are part of a healthy immune system. Another possibility is a sebaceous cyst. If the 'lump' enlarges or becomes painful you should get seen.
Mass under the chin. The most common cause is acne infection in the skin of your chin which causes the submental node to enlarge. Sebaceous cyst are also common at this location. See an ENT doctor.