Four days ago, i got a new tattoo on my right calf from a reputable shop. today, however, i noticed a swollen lymph node in my neck, on the same side.

Unrelated: The more familiar you become with your body, the more you'll notice lymph nodes coming and going. In fact, the excitement of getting a tattoo (I have three) changes your levels of cortisol and this may have redistributed your cells that fight infection -- that's speculative. The vast majority of lymph nodes are your friends. Best wishes.

Not related: An infection in your calf would not go to a lymph node in your neck. Look for a tooth or gum infection. Best to see your dentist and if he finds nothing then your doctor.