I have exactly the same thing. Enlarged posterior cervical. Gp examined mine a couple of weeks back and told me she was sure it was nothing more that a shotty lymph node ( lympb node that has remained swollen after infection-normal. I have been worried about mine as well. GP did take my bloods and they were normal so I would hope that lymphoma would have showed some abnormalities there. Mine feels just like yours. I dont know how long mine has been there but I did notice it about 3 months ago.
Try not to worry,and if the nurse couldt feel anything then thats ok. Have you asked Gp to check it out for your peace of mind
sharanjXX