Hey, honestly you could make this decision so much easier for yourself if you do just a little bit more research
1) Watch YouTube videos about life as a doctor and life as an engineer, read about the different careers in medicine and engineering, find out about the working hours for both. Doing this will help you decide which path you are really interested in
2) Physics and Chemistry are both equally challenging. However, it helps if you are interested in either one of them. Look at the course content for each of them and see how you feel about them - find the specifications online and compare them
3) How do you feel about Maths? If you are really, really keen about maths, then lean towards Physics. If maths is not something you've ever really enjoyed, Chemistry would be better
4) Maths and Computer Science go well with Physics and Further Maths because they are all very quantitative. My subject choices are Maths, Further Maths, Physics and Economics and they complement each other very nicely but they are all very difficult and require a lot of studying. With these subjects I can do a degree in most fields of engineering, finance, economics, law, business, maths, physics and a lot more. The thing that motivates me, however, is that I know exactly what I want to study at university and the career I want to go into - this allows me to commit myself to my studies no matter how hard they get