Hello, I'm Dr Gary. I've been practicing veterinary medicine since 2007. I look forward to helping with your questions/ concerns.
It sounds like your dog has swollen lymph nodes. They are found under the chin on both sides, just in front of the shoulders (hard to palpate here) and behind the knees in the rear limbs. If they are all enlarged, or were, then the most likely cause of this is Lymphoma
, a type of blood/ lymph cancer.
The diagnosis of Lymphoma is made by getting a needle aspirate of the glands and looking for cancer cells (lymphoblasts).
Treatment for lymphoma is with chemotherapy. There is a University of Wisconsin protocol that has good results with an average of 12 months survival time. Without treatment, the survival time is only 2-4 months.
Other differentials are infection, most notably tick born disease. If the aspirate shows inflammation as opposed to lymphoblasts, then I would go with a 10 day course of Doxycycline
most tick born diseases.
I hope this helps, let me know if you have any other questions.