Hi and welcome
HUGS
I am very sorry.
No guinea pig owner wants to hear about swollen lymph nodes because of the spectre of lymphoma - cancer of the lymph nodes. It is incurable. The most aggressive forms can mean that your piggy is dying or may have be euthanised within days or a couple of weeks, depending on how advanced it is. With milder forms and corticosteroids, the lifespan has been in some cases extended to a few months, as some members with more recent milder cases have proven.
There is unfortunately very little information (never mind research) about cancer in guinea pigs. The most common of them is lymphoma.
This is the best overview I have found:
Can guinea pigs get cancer?
However, since you have more than just one swollen lymph node, it is unfortunately rather likely that you are either dealing with a more advanced form of infection or more likely advanced lymphoma.
I seriously wish that I didn't have to be the one to break the bad news to you that nobody else wanted to tell you. We cannot tell you for sure and can only go by our own and our collective experiences on here. Only a biopsy and lab test could tell - and if you are
really unlucky, your piggy may not even be there by then anymore.
We can however be here for your piggy and you as a community both with practical tips, personal experiences and with moral support for however long you need it - other than social media. I know that it is a lot for you to take in right. Please be kind with yourself. Lymphoma is not something that is down to bad care and it is not your fault. It can and has happened to most of us long term owners at some point.
You may want to enquire about painkillers. We are UK based (although with members from all over the world) and have much stronger legal restrictions in that respect compared to the USA once pain takes over the appetite and you will have to start having to think about quality of life.
This is a guide I am never happy to link in but you may hopefully find it helpful:
A Practical and Sensitive Guide to Dying, Terminal Illness and Euthanasia in Guinea Pigs
My thoughts are with you and your precious piggy. We are here for any questions that you have along the way, as well as for moral support.