In every clinic does a doctor give you a different medicine you ask for?

In my country, usually, the doctor is the expert. We pay either by taxes or privately for that knowledge. Why tell the doctor how to do his or her job? Many people ask for drugs that have no effect on their condition, very often antibiotics. The doctors are right to refuse these.

Excessive antibiotic prescription is a big problem in my country. People think they are magic pills for e.g. baby's cold or whatever.

Not if you are being honest with them; which, you should be since, many prescriptions don't intermingle well, often to the point of death.