Question
Dear doctor,
I started having a pain in my right flank, exactly in one of the last ribs.
I feel this pain only If I press or when I sleep on this side.
I went to the doctor and he did ultrasound which was fine and blood test too. The pain started in december 2010 that is 1 year n 6months now.  
I am still feeling this pain and I becoming worried because I cannot find the root of this pain.
I am a girl of 21. I am a student in the university. (I though t you'll need this information).
I appreciate your time and consideration.

Answer
It could be several things.
A: do you have scoliosis ?
B: did you have trauma or sporting accident to the ribs or back?
The ribs attach to your spine and you should have a check up. A chiropractor is well equipped to deal with this type of problem as long as its not something else internal.
Good luck!