You will need to check on the specific regulations in Pakistan. In the US a medical doctorate (MD) is only offered after at least 4 years of post-graduate schooling so many people will get an undergraduate degree in engineering and then go on to medical school. In some countries like India, and I think also Pakistan, medical training can be undertaken as an undergraduate degree so there is no need to get an engineering degree first; however, there may be options to double-major. I don't know how that training is regulated. You will need to inquire directly at the medical school that interests you.
As far as biomedical engineering, it is not the same thing as medical training, although some of the materials may overlap. A biomedical engineer is an engineer who works on medical problems so they need some of the same training in physiology and biology that would be expected of a doctor, but they also need a firm understanding of engineering. Someone who achieve a PhD (Doctor of Philosophy) in biomedical engineering may be called a doctor, but it is not the same thing as an MD and not a license to practice medicine.