What would cause posterior cervical lymph node pain and swelling? R neck is swollen, pain from base of skull down to front of neck/throat

Many possibilities. There are a variety of things that could cause these problems at your age. Infections(cat scratch disease, mononucleosis), dental /sinus disease), are most often the cause. However, more serious problems occur in this age group. Please see your internest, ent. Or oral/maxillofacial surgeon asap.