Hey Leanne
I sympathise with what you're going through - I went through similar stuff and what everyone's saying is spot on - you have to go armed to the teeth with knowledge, questions and a minimum outcome that you want from the appointment.
It can be tricky getting them to take you seriously at first, but when they realise you know your stuff and aren't going to be fobbed off anymore, they usually do what you want!!!
Keep at it and remember, we've all been there and we know how angry it can make us! Stay focussed on what you want out of the GP appointment (book a double appointment if you have to). Oh, and write EVERY THING DOWN! (Assuming your memory is anything like mine anyway!)
There IS light at the end of the tunnel, so don't give up hope!
xx