I would imagine that the doctor DOES believe that you are clinically depressed for them to prescribe an antidepressant. I don't know where you are from but, in the UK, GPs are told to prescribe anti-depressants only for those with moderate to severe depression (that's not to say that those with mild depression don't get anti-depressants sometimes because GPs can't be bothered/or don't know that 'watchful waiting'/counselling is better).

Personally I would not take any medication that I didn't know what it was being prescribed for, common side effects and how long I might be expected to take it for. It is your body shortandcute - you are allowed to ask questions about your health! Also I can not recommend therapy highly enough for depression.

All the best,

*Willow*