My 2yr old has large swollen lymph node in right of neck that is increasing. doc says if it gets any bigger he will need tests? why? he isn't poorly!?

Hard to say: The doc had the benefit of an exam, which does provide some important information. Most nodal enlargement peaks within a week or so and declines over a 3-4 week period if the nodes are working correctly. Sometimes they need antibiotic support to kill the germs within, or need to be drained. Sometimes they are a signal to a more important condition that tests would define.

Swollen gland: you have to check for infection or cancer if the node enlarges