My brother-in-law has spotted lymphoma before. He said when they suspect something like that, you get a battery of tests ordered at lightning speed - often same-day.
Now, I want you to think about this in a different way. Imagine one of us was posting this. This person - let's call them HAgirl - has a couple of small, movable lymph nodes that don't really seem to be growing. (One might be sore-ish, but HAgirl has been touching them non-stop.) HAgirl has had multiple blood tests, all of which turned out normal. And every doctor she's seen has said they're fine. Yet HAgirl is convinced she's right (even though she doesn't have a medical degree) and every test and doctor is wrong.
What would you say to her? I know what the answer is, and that is what you need to say to yourself every time you start worrying.
Something that also helps me: make two lists. In one column, write a list of probable benign causes for your symptoms (mono, cold, virus, anxiety, allergies, etc.) and then make a second list of all the reasons why you don't have lymphoma (multiple tests have ruled it out, no doctor thinks you have it, no real symptoms) and force yourself to read through them every time you feel nervous.