If you don’t have a ton of medical experiences due to your interest in medicine being relatively new, you can and should focus more on what qualities you have that show why you will be a good doctor. Think about experiences in your life, whether medically related or not, that showcase your strengths that will make you a great physician—compassion, resilience, creativity, empathy, curiosity, dedication, leadership, etc. A friend of mine spent a good chunk of his PS talking about how difficult it was moving to the US in high school and how he had to adjust to a new culture, teach himself English, etc. Although not medically related, it conveyed many good attributes that he has developed and painted a great picture of him as a person (novel idea for a personal statement, right?). You will want to make sure you pepper in and/or create bookends to your essay that reinforce the “why Medicine?” part, but the meat of your story is more flexible.