Not really sure where to start...

For the past year I think I have been suffering with depression. I want to go to my doctors about it but not sure what to say when I get there. I'm scared that they are going to think I have made it all up and that they're not going to believe what I say. I read somewhere before (not sure if it was this site or not) that making a diary of thoughts and feelings can help for when going to the doctors but not sure how to approach it and what to include. If anyone has any advice or suggestions on this I would be grateful.

Thanks,

Alice