Swollen lymph nodes are not something that should or can be diagnosed over the internet.
Swollen lymph nodes are a sign that something is wrong in your body. This should be combined with a complete blood profile with white blood cell count, etc.
It could be a virus, a low grade infection, etc. Swollen lymph nodes are NOT usually caused by allergies.
You can probably test that by taking a histamine blocker like benadyl. Once a histamine reponse is blocked, there is little chance of inflammation getting thru that (at least temporariily) because your body will not be able to produce much of a histamine/allegenic reaction on benadryl.
I've spent more time in immunologist/allergist offices than most people so I do know some stuff.
All that said:
3 months is a long time to have swollen lymph nodes but only someone trained to palpitate them (to see if they are hardened, fixed in place, moveable, etc.) can
If you do not have insurance then you should go to your local DHS and see if you qualify for medicaid. You should also at least get to a walk in clinic........y
ou can ration food, ration gas, and ration vape stuff but your health is always the most important thing.
The blood tests will be sent to a lab, and you can pay THAT bill off month by month.
You did not say where they were but ANY low grade infection can cause this, even a bad tooth. It could be in sinus, or anywhere in your body. Please don't be "scared to death". Very few swollen lymph nodes are cancer.

Most usually this is something that needs to be fixed with anti-biotics.
You do not want to mess w/your lymph system, it is your #1 immune system defense.
Please, do go see a doctor.

Find a "doc-in-the-box" and just go. Soon.