Swollen lymph nodes but no infection doc says, on amtrymitline for headaches, but what is hard lump behind jaw under ear if i have no infection?

Lymph node: You probably have a lymph nose on the mastoid process. A bony part behind the ear. Have an ENT look at it. They will sort the problem out. Good luck!

Monitoring Centers: Lymphatic system absorbs/carries things too big to go into the arteries/veins like bacteria eaten by white cells and digested food. Lymph nodes "taste" the lymph for anything bad like bacteria/viruses/cancers, etc. When it detects a problem, it alerts the immune system and your body reacts. They enlarge in response to the inflammation they create when they react. They shrink when all is well.