IMO if the only reason you would want to continue doing physics is Medical Physics, I'd suggest against it. Our school does the medical physics option and there's really little relevance to anything in medicine. It's mainly just learning about diagnostic techniques and an outline of the physics of how they work ie ultrasounds and the refraction/reflection of an ultrasound wave (almost no discussion of any health issues mainly how they are diagnosed and the depth of this tbh isn't great either it's more of an outline). I don't really find it too interesting and to be honest there aren't many universities which require any of the sciences as prerequisites for the medicine course.
In the end it's your call, the syllabus is also changing not sure by how much but yea again if you're not enjoying physics right now I don't think you will enjoy year 12 physics.
I'd suggest not dropping physics as soon as the HSC course begins though you might change your mind. Maybe wait a while until you drop it, discuss with your teachers etc
Sent from my iPhone using Tapatalk