Here is a recent article from Science Magazine outlining some of the many options available to become a doctor focused on understanding why people get diseases and what treatments can be developed to help them. Getting into programs such as the MSTP or PSTP, or simply choosing a medical school that allows research electives is a good first step, that can be followed by careful selection of research-friendly residency programs designed to help you with the transition from post-doctoral/post-graduate trainee into an independent assistant professor.
Scientist, Mother, Physician, Educator. My first paper was on neural programs that control fish feeding, later wandering through macrophage antigen "nibbling", to my current interests in brain autophagy (cellular eating of damaged or unneeded parts).
Science is fun!
If you are curious about how things work, or have ideas on how to make things better, science may just be for you. The nature of research is that you do not know the outcome of your experiments until you do them. The most rewarding moments come from the unexpected results -- that moment of inspiration when you discover a new way to fit things together and new questions to ask.