Thank you for posting your query at DoctorSpring.com
You have an enlarged neck node, you had sore throat last week. Most of time node occur following infection of throat and nose only and it may persist for some time. But if it is not improving or increasing in size that we can do following investigation-
USG or ultrasound neck to see size shape and content of node.
If require we can do FNAC , that will provide diagnosis and rule out cancer.
With this presentation in young age cancer is very unlikely.
Hope this helps
Dr. Sunil Jalan