Hi Claudia! Only you can decide what fulfillment feels like and looks like for you.
That said, you will find many people who get joy, satisfaction and a sense of purpose by doing things in service to others. It seems like you are already thinking about that by asking about Occupational Therapy, so no matter what approach you take, you will already be in position to serve others - all the time!
One thing that might help you answer the question for yourself is to reflect on your current 'work' (school & studies). Do you find yourself energized by deeply understanding one subject? Do you spend your own time researching beyond what is covered in class? Or are you quick to grasp a concept at the basic or core level and then energized by moving on to the next?
If you're not sure, maybe start a log or journal to reflect on the things each day or week that you lose track of time on and those things that seem to drain you or you avoid and procrastinate on. After a few weeks, you should start to notice trends. Once you do, it becomes a lot easier to look at job roles and careers through a lens that will tell you if it will likely feel fulling and energizing.
Hope that helps!