Indeed, the OP should be receiving a much faster response from the GP, 10 or 12 days is a ridiculous length to have to wait. Personally, if that were typical for my issues I'd seriously consider changing to another practice.Unfortunately that sounds about par for the course these days. The NHS might be ok for physical ailments (if you can actually get into the system), but it is absolutely crap regarding mental health.
I can't see how being "functioning" make any difference, other than it means you are still breathing. I would get back to the surgery, stress your symptoms and insist on a quicker appointment - preferably face to face. Phone calls have become a cop-out and are not nearly as useful. If you can get in there, the GP will (probably) be sympathetic and may even help. Don't be abusive to the receptionist, because regardless how obstructive they seem (and are), they are only doing what they have been told. You don't want to get kicked off the practise list
Are you on any prescribed meds for this already?