Hiya, i'm not sure i can be of much help really because i have no experience of lymph node swellings, When you say your anxiety is keeping you awake at night .... trust me that is normal. We all have fears and anxiety which does that to us, then we worry about worrying and worry about not sleeping, it's a vicious cycle but you have done the right thing by making yourself a GP appointment. I think that after hearing your grandmothers story then this is also playing a big part in how you are feeling right now. 

I am not saying this to scare you by any means but sometimes having an illness, any illness not just Cancer does not necessairly mean you have symptoms. I remember visiting my GP about 3 years because i felt unwell (i am not a regular doctor visitor by any means, in fact i hadn't been in around 2 years) and i have a history of severe depression and anxiety, anyway, i couldn't pinpoint my symptoms but told him that i knew my body and i knew something wasn't right, well he sent me away with a flea in my ear and said "Miss G, people like you present themselves with problems that are not necessailry there" I left in tears and vowed that i would never go back to him, look at me now, diagnosed with lung cancer because i wouldn't go to my Doctor for fear of being called a hypochondriac so while me reply to you may seem a bit long winded there is a point to it. If you believe that something is wrong then be persistent, ask for an explanation as to what it could be, why they won't send you for tests, keep at them, be persistent if you genuinely believe that something is wrong with you.

Oops, sorry about that, i've had a glass of wine and i got carried away with myself  and wrote the first chapter of my new book, lol, but what i wrote are my true feelings but i really do hope that someone with more knowledge of lymph node swelling comes along and can give you some proper advice. 

PJ