Why do I have so many swollen lymph nodes?

[scmommato3]

Back in August I began feeling unwell followed by swelling of my lymph nodes which began under my arms, then groin area, then neck. My symptoms include:
Headache
Stiff/swollen neck
Feeling like I have the flu
Fatigue
Nerve pain
Shock pains (back area)
I did have an MRI of my spine (neck and upper spine) and though my lymph nodes are palpable, they were not enhanced or enlarged on the MRI. I had a biopsy of an axillary node in October and it was a "fatty node." I have no idea what this means. I am not overweight as dr. Google would suggest.
I'm just wondering what would cause all these lymph nodes to swell up and stay swollen for so long if it's not lymphoma. My dr doesn't wish to investigate further because I have a normal blood count and biopsy. I would get a second opinion but he is my 3rd opinion. He did say that he could feel the nodes but they weren't "overly big" do just keep an eye on them. I'm also wondering if I might have Lyme disease as I used to run in the woods behind my house and did brush a couple of ticks off of my clothes this last summer. My doctor didn't want to run any more tests.