This is of course a critical situation because you lack interst in PCB in your current class twelve but it is the insistence of your father for taking up such subjects. This situation of ambiguity would not help you ultimately and firstly you need to take the rout of self introspection analysing the merits and demerits of each combination.
PCB is your combination in your class twelve and you are fully aware of the course materials. With your sound concept in such a combination, you can go in the medical lines after facing the entrance test in the Medical. The second option could be your persual for any one of such courses such as Biotechnology, Biochemistry, Microbilogy in your graduation level and your success would depend upon your attitude and passion.
Now you say you have fascination with the commerce stream. Let us investigate the course of structure of B.Com including Accountancy, Finance, Economics, Bussiness Administration etc. apart from a language paper say English. What are the subjects for which you have some special inclination ? In this context, I would like to add that without the fundamental grasp of Mathematics dealing with Differential Calculus, Algebra, Trigonometry, Arithmetic, Vector, Integral Calculus and so on, it would be difficult to go ahead with the subjects included in the B.Com course. Analyse each point critically before you come out with a final decision.
Once, you are clear with your thoughts, initiate a dialogue with your father and put up your views before him regarding your choice. Mind it either of the courses is not easy or difficult and your success depends upon your interest, aptitude and your intense passion for either of the combination. Convince your father that commerce stream would suit you most.
In the meanwhile, look out for a tutor providing you inputs in the commerce stream especially Mathematics
Yes, you can persue B.Com course but for that you will have to meet the admission committee of the different colleges and you may be considered if there exists a vacant seat.