My mom tells me stories about my medical history that are hard to believe. if she makes up a story, what could be causing her to do this?

Believe her: You must first be sure that her stories are wrong and then you can start to worry about her.

Munchausen's : I don't know whether what your mother is telling you is factual or not. However, in the condition called "munchausen's syndrome by proxy, " a parent can present a child for care with certain knowingly manufactured symptoms. In such illnesses the purpose is to assume the role of patient/ill person and not to avoid roles or duties. It's also an unconscious process, different from malingering.