Hi.. Thanks for the query.. It looks like the lump under the neck is a swollen lymph node that can be probably due to inflammation caused post tongue piercing.. As stainless steel is also an inert material so chances of it causing any allergic reaction are less.. So it is advisable not to disturb your piercing and leave it as it is and just maintain a good oral hygiene and do cool compresses over the lump. Also take anti inflammatory painkiller like Ibuprofen.. If at all you see any signs of infection over the piercing site or there is increase in the size of lump then first get it clinically examined by a Physician and then only proceed for getting it removed or re-piercing with titanium.. Hope this helps.. Regards.