4 year old son has swollen crevical gland for 4 weeks. oral thrush after 7 days nystatin getting worse. should i be worried?

Follow up w/ his Dr.: You should follow up with his doctor. Depending on what's already been tested, you may need to have blood tests to see what could be the potential cause of this. I screening CBC & perhaps a test for the Epstein Barr Virus may be a good starting point, but it depends on his current physical exam and knowing more history than is provided here.