Hello, My 8 Years Old Son Complained That He Has

Hello, my 8 years old son complained that he has a sore throat a few days ago. I gave him Motrin for a couple days. Then I start noticing the change in his voice yesterday. He said it still bothers him a little but it not as much. Today I asked him to open his mouth and I saw a swollen gland in his throat. What should I do?