The previous drug use could be the cause of your mood disorder. He could be just asking you what diagnosis you prefer so that he can write authority scripts and help with medical certificates/disability etc. I get where your doc is coming from, this is drug induced illness so it is hard to put a label on.

If you were in the US they would label you bipolar and kick you out the door with a boatload of drugs which can affect your mood greatly and cause more problems. So be thankful for that.

Go for the second opinion but remember it does take more than one session to be diagnosed correctly. Are you in therapy too? We can get up to 12 medicare covered psychology sessions a year. It could really help you out.