Thanks for query,
The swelling on your neck on tattoo is a Lymph
When we gets any type of inflammation we gets the regional Lymph gland swelling of that region that will subside by its own when inflammation subsided or some times it gets infected.
In your case it may be due to your tattoo or may be due to your Tonsil
infection & as it will not swollen it may subsided by its own or not increase more.
if its size increases or it causes pain you should consult your doctor.
Your mucus in throat may be due to your tonsil infection.