It is normal for a tattoo to be a little tender and swollen for a few days after having it done. Usually, however, this is limited to about the severity (in terms of redness, warmth, and pain) to a sunburn. Definitely the area of redness should not spread much beyond the actual tattoo.
The fact that you have a swollen lymph node is concerning. As you know, the lymph nodes are involved in draining infections from the skin and other parts of the body, and the lymph nodes behind your ear do drain some of the skin of the back of the neck. So, having a swollen gland here could be a sign of an infection.
Other signs of infection to look out for would be worsening pain, spreading of the area of redness and warmth beyond the area of the tattoo, and fever
. This type of infection, which is an infection of the skin, would be called cellulitis.
It is advisable that you see your primary care doctor
or even an emergency room doctor to have the area checked out and to make certain that it is not infected, as you may require antibiotic therapy to clear up the area in the case of an infection.