Hi there Soso.  It is not possible for anybody here to diagnose on this website; apart from the fact that we don't have any medical training anyone  (preferably a doctor) would want to examine the lump and ask questions before even thinking of making a diagnosis.    It could well be just be piles but as stated I cannot make a guess.   Even if it is something relatively harmless as it is causing you discomfort (and worry!) I would recommend that you go to your doctors.  Don't know if you have tried pile medicine over the counter(and to be honest I don't know how good it is) but the only sure way of dealing with it is to visit your gp.  Best wishes.  Annie