If you're prioritising med, then I'd recommend keeping Chemistry. Chemistry is also a 'recommended study' or 'assumed knowledge' or even a prereq in plenty of engineering streams as well, from what I've been reading from a Year 10 UAC booklet I received last year. And if you are prioritising medicine over engineering, I would also suggest you keep Biology -- you said you really like it, so it's really a no-brainer to keep over Physics, in my opinion.
Also, genuine question, why are you considering engineering despite not liking physics or chemistry? I could be wrong, but it suggests to me that even if you make it into engineering, if you don't like physics or chemistry (two courses that are either prereqs, assumed knowledge or recommended studies in engineering) that you may not enjoy the course.
(It also might be too soon, since it's only the start of the year, but I also could say just try each three sciences out, track your grades in each of them and how much you enjoy each subject, then make a more knowledgeable choice at the end of the year when it's time to drop down)