Lump

Hi, From my childhood, I have a small growth on my buttocks( near to the anus ). It was small then. I had also consulted a physician in India abt 10yrs back and he took some samples from the lump for testing and told me that nothing's there to worry. He also prescribed a medicine, after I took that medicine, the lump completely dissappeared. After couple of years this lump came up again. Now in winter when its cold this lump will become little big and will start to pain and in summer it will go back to its natural size( though little bigger than what it used to be before I took those medicines ). Now Iam in Ireland on a small assignment and its winter here and this lump has started to pain. Sonetimes I have difficulty sitting. Please advise me on whether this is something that I need to take up with high priority ? Is there something that really has to be feared about.