Painful Stomach Lumps

My mother has been complaining about painful lumps in her abdomen that she says feel like two "baseballs" inside her.  At first, they were not painful, she could just feel them, but now they are painful after she eats or whenever she is active for a long period of time.  She has had blood tests, x-rays, and has had 2 CATscans done and no one can give her an answer...they say that the "balls" don't even show up on the tests...like if they aren't there and she is making them up.  I am scared because the lumps are becoming more prominent and painful and I am fearful that they may be tumors.  Anyone have any answers??  Please help.