Swollen posterior cervical lymph node

Hi there, 

I have a swollen posterior cervical lymph node on the right side of my neck at the back but it can only be seen when I turn my hesd. I went and saw a GP and she said that they were fine, do you have any idea what this lump could be? It's small and fairly firm but there's no pain with it, it's been up about a week now. I am currently coming to the end of a throat infection/ viral tonsillitis but I didn't think that would bring up the lymph nodes at the back? 
many thanks