Definitely see a specialist. A psychiatrist. I read all your posts and you've been suffering for a long time and wondering what is wrong.
What to do: Just show the doctor this thread. Your first post at the top. And make a list of symptoms you feel...you've described various ones. Thoughts of death, feeling like you are meant to be sad, paranoia, etc. It's nothing to stress over - but I know it is hard. I assure you they won't be shocked - they have heard it before, be honest and don't hold back.
I'll share what my psychiatrist told me - he did diagnose me (see my signature) and he said a diagnosis is needed to optimally develop the best treatment plan for the patient. BUT, he said treating the symptoms is what really matters. It's true. It's not the label, it's knowing if you have a condition/illness, what it is - and then receiving help to ease your symptoms. I think there's an excellent chance you can feel much better IF you get evaluated and treated.
Please go get evaluated by a psychiatrist and keep us posted. Your GP and therapist don't sound qualified to diagnose you. I have experienced many of your symptoms and it could be any number of conditions. Time to find out, it will be OK. You can keep it private or we can support you if you keep us posted. I am certain that there are others that will be able to relate and we never judge. You've been here long enough to know that. =]
Your posts question over and over what is wrong, etc. I have a lot of ruminating thoughts from an anxiety disorder. Do you think over things ALOT, on other matters, too? Either way, I'm happy you posted. Yes, you sound anxious...anxiety doesn't feel good but it's not harmful. Get an appointment, please go!

Get a name for a psychiatrist from your GP or therapist--you can do it.