My mom came in with me to the pediatric exams until the age of about 12/13. It was my last exam before transitioning to Highschool, where it was also no longer considered appropriate for parents to sit in. That specific last exam with my mother being present, also happens to be my first physical exam that I can actually remember very well. I remember having to undress down to my briefs while my mom was chatting with the doctor about my file. Then I was measured and weighted, had to walk around the room, stand on my toes, heels, on one leg, and so on. I was a rather shy boy, but I remember that I felt some level of exitement by all this attention for my body, while having to walk around almost naked in front of two fully clothed adults, of which one (the doctor) was a total stranger to me. Then I had to come and stand before the doctor and he directed me to blow as hard as possible on the back of my hand. To my surprise (at that time), he then gently pulled down my briefs to my ankles and took a long stare at my exposed genitals. I'm not sure what exactly triggered it this first time, but while the doctor took his time watching me, my penis quickly started to uncontrollably grow to a full erection. I felt rather embarrassed but the doctor did not seem to mind and without saying a word, he gently started to feel my balls and erect penis. Luckily my mom was sitting behind me at the back of the exam room and could only see my bare bottom. When the doctor was finished, he carefully pulled up my briefs again, covering up my erection before my mom could notice. I still remember that I had to admid that it felt good when the doctor had touched my penis, and I often fatansized about it in the days/weeks after. I also liked the idea that there was this kind of 'little secret' between the doctor and me in which he had privately seen my erection without anybody else knowing.
In the years after, based on this first memory, I kind of knew what to expect at the schooldoctor and always had an erection already up front out of anticipation. I'm not sure by what I was triggered the most. Maybe it was because of having to be (almost) naked in front of a clothed stranger or maybe it was because of loving the feeling of being (intimately) touched. However, certainly at that age, it also always appeared to me that the build up of pressure in your belly when instructed to blow on your hand, somehow contributed to getting an erection. Actually, for quite some early years at the schooldoctor, I believed that the purpose of the whole thing was to get an erection such that the doctor could examine it.....only much later I was told that it actually was used as a hernia check.