I'm glad you took the note to your GP this morning, and that he actually gave you a longer appointment. He seems like a good doctor you really should listen to him when he says to call if things get worse before the two weeks until your next appointment. Even if you just go and let him know how it is getting it off your chest might help.

With your therapy is there anyway you can increase the sessions to weekly instead of fortnightly? Maybe that would help to give you more support right now. And if the doctor recommends this IAPT (no idea what this is) then theres no harm in trying.

And he is right, this is absolutely not your fault. We don't choose depression and everything that comes with it. Don't blame yourself or beat yourself up over it. You're doing the best you can