<s>[INST] am a 24 aged female. i hv been suffering terrible pain in the end  tip of my back born 4 the past 1 week and more. i dnt knw what that portion is called to specify the area where i hav pain. it seems like sweling there.and i fear the sweling portion is full of puss or smthng like that. i dnt knw.. [/INST] Hello, I had gone through the case and found that this is called as tail bone or coccyx. I will advise consulting to orthopedic doctor for swelling. It might be muscular swelling or filled with pus. If there is pus then go for blood test and biopsy of lump. If only muscular swelling then go for MRI of lumbosacral area. After the proper diagnosis take treatment. Hope my answer will be effective for you. Thanks </s>