Hi Brianna, My first thought with such a young puppy would be infection which has caused the nearest lymph node to become swollen. You're right I wouldn't have vaccinated puppy until this issue was resolved but the swelling appears to be resolving with the antibiotics and he sounds like he is recovering okay. I don't give Lyme but then I don't live in a high risk area but even so I would not vaccinate for that before six months of age. My preference is not to vaccinate whenever there is a health issue apparent and not all vaccines need to be given at the same time.
Before thinking cancer think of infection first. Wenever the body is reacting to bacteria the lymphactic system gets to work overtime and glands can appear swollen and tender. If glands do not subside and have a woody feel to them then they need to be biopsied. Rose T.
