welcome to HealthcareMagic
Like you said doctors are quick to prescribe medicines without investigating some people say the exact opposite that the doctor run so many test then they prescribe the medicine.Please understand :-
1-the doctors study for years through books;patients about diseases;the signs and symptoms so when a doctor takes history of a patients disease he can analyse many diseases which are common and so the doctor quickly prescribes medicines.
2-Whenever the symptoms are not clear or the patient is not responding to the treatment there is need to do investigations.
example of a case of malaria-malarial fever
is normally high grade fever with chills
and headache so the doctor can give treatment for malaria because even simple test of malaria which is a peripheral smear is not always diagnostic of malaria.But if the patient has a mixed infection of typhoid
and malaria the malaria may go away but he will still get fever because of typhoid and since the fever is not going down the doctor will advise investigation for it and once typhoid is diagnosed he will prescribe the necessary antibiotics.I hope i have answered your query.