Hi my name is Kyle and i'm 17 years old. I have always found swollen lympth nodes and can recall first finding them at least 5 years ago. Now and days I have several throughout my neck that I can feel some on both collar bones. I have gone to the doctor and had tried to have them felt, but the doctor can never feel any of them except one. I am freaking out and suffer from severe health anxiety and sit here thinking that I am getting sicker while my doctors arent finding anything. I have no other symptoms other than swollen nodes.
I would say you should go to your local walk-in clinic or A & E this week for a second opinion from another health professional.
Have you read this leaflet?
https://patient.info/health/swollen-lymph-glands 
You say you have found swollen lymph nodes for the past 5 years, since you were 12. Surely your parents took you to see a doctor, what did the doctor say? Do you live at home now Kyle? Ask one of your parents to go with you to see the doctor.
Hi Kyle, There several ways that Doctors determine if someone may have a type of cancer. A complete blood test is one way. Most things will show up in the blood.
Also, the Doctors will ask about symptoms. Certain symptoms point to specific illness.Swollen lymph nodes can be caused by Mono and a few other things.
If your Doctor has taken tests according to symptoms, and you feel good, you need to stop worrying. My grandson was like you, but he thought his bones would fall apart because he couldn't drink milk due to allergy. We explained to him, that calcium is also in most vegetables. Hope you can stop worrying.
harrishill