When will the pocket of fluid in my lower back go away? (photos)

After reviewing your long RealSelf file I question the judgement of going to the DR for additional surgery. Now you have a recurrent seroma than needs insertion of a closed drainage system. Since you already used Dr C. Mendieta, why not return and pay for the minor drain insertion surgery with him? Or is he refusing to see you? Than next option is fly back to DR for this surgery. Or if I were to offer care my fee would be a global $2,000 for operative re insertion of coccyx drain and all the follow up care involved. It seems the cheaper way will now become quite expensive. Sorry for ALL you issues. 

Thank you for the picture.  You need a drain placed to treat your seroma.   You also should call the surgeon that performed your procedure even though he/she is not local for guidance.

You likely have a seroma, although it is difficult to tell.  It could just be swelling.  Without examining you and knowing if surgery was done in that area, it is hard to give you better advice.  If it is a seroma, it could respond to drainage and compression.  Please let us know if the area had liposuction or not.