Hi.. Can understand your concern.. As per your complain if you have pain in the gum below the tooth that was filled 3 months back there may be a few reasons for it.. One can be that when the cavity was made to clear off the decay, some portion of the infection must have left out and filling was done over it. Now the infection that was left out furthur progressed and reached pulp that is central portion of tooth containing nerves and blood vessels and through there to the root canals inside roots and finally reaching the bone below root tips causing infection and pus formation which causes pain on touching the gums.. Other reason can be that there could have been some leakage through the filling causing seepage of food debris below the filling and thereby causing infection which infects pulp and progresses below root tips and causes pain and pus formation.. One more reason can be that the cavity made for filling is drilled so deep that it has inflammed the pulp and causing pain. I would suggest you to consult your dentist and get an IOPAR ( x ray )done so that the exact cause of pain is understood.. In most circumstances of pain in tooth after filling the treatment to be carried out is ROOT CANAL TREATMENT in which entire pulp is extirpated and filling is done in root canals as well as crown of tooth... Hope your query is solved. Thanks and regards.. Dr.Honey Nandwani Arora..