HI. A lump of such a long duration would have been removed if it was a sebaceous cyst. If your Doctor had thought of a lymph node FNAC would have proved what it is. Now it is growing since one week and is extremely painful suggests that there is an infection. Since antibiotic is not helping , you may need to change the antibiotic and add a strong anti-inflammatory medicine which helps to reduce the pain also. Another option is to go for surgical incision and drainage and please request your Doctor to go for histo-pathologiacl diagnosis also. This will remove the pus, the lump, gives you immediate relief and a perfect diagnosis to carry on further treatment if needed.