GPs shouldn't be left to deal with depression at all, but unfortunately they are.
Psychiatrists are the ones who are actually properly trained in getting the meds. just right for each individual they treat.
If your depression is substantial then you ought to see a psychiatrist. Is all it takes is to ask your GP for a referral. If you feel you can't afford it, then you can probably access them as an outpatient at a public hospital.
Doesn't sound like a good idea to be self prescribing the dosages you take either. What is the point if it is sub-clinical?
