I'm really worried about my sister. She's been coughing for the last three months, and it just keeps coming back. On top of that, she's lost weight compared to what she used to be. When she coughs, she feels pain in her chest, and she's also lost her appetite. She's mentioned having a bitter taste in her mouth too. A general physician advised her to get a chest X-ray. Can you help me understand what might be going on? What could possibly be causing all these symptoms?