These are just some cursory corrections; I will be able to look at the essay in greater detail after this week. So, i will try to give you more of a substantial feedback, then. But here is something to start you off;
As a child, I was in and out of the hospital so frequently that some of my earliest memories involve my being around the hospital bed. My childhood amusement often entails a game of role-play with my toy stethoscope, a syringe and a tattered doll, which would be adequate for my practice of medicine. This may have originated my fascination with health and science, it was no surprise that I decided to study biology at University of Toronto and later specialized in immunology.
I really liked your first sentence. It certainly had me curious as to why you spent so much time in the hospital and i admit, i was expecting the next line to give some sort of an explanation. So, when you started to talk about your childhood amusement, it threw me off a little. Maybe you could add in another line to describe why you were in the hospital so often?.....OR just start off with "My childhood amusement..."
"These games triggered my fascination....science, hence, it was no surprise...."
hope this helped and I'll go through the other paragraphs soon.