I understand you had Botox performed about 10 days ago. Nevertheless, it is unusual to have Lymphadenopathy. Lymphadenopathy is a rare side effect of a BOTOX injection, caused by local tissue trauma in the area of injections. However, it's also possible that there are other reasons for your enlarged lymph nodes. Many other factors may have caused the problem, and they just happened to occur around the same time of your BOTOX injection. Things as simple as a common cold, a local infection, or a hot cheese pizza burn on your inner cheek can lead to an enlarged lymph node in the head and neck area.
I would recommend, if this lymph node is accompanied by fever and tenderness as you described, that you seek out medical attention from either a board certified internal medicine physician or your dermatologist.