how to approach gp about depression/anxiety??

I'm shy awkward and can find any excuse not to go get help but I'm fairly sure I need it at this point. I've been on the floor in tears, I've had no motivation to move I've injured myself I can't put others through this. But how can I approach this with a gp, how difficult is it to diagnose things like this. Would I need more than one appointment?? Its difficult enough trying to get out the house with my mother who doesn't believe in depression or similar mental disorders.