Appealing ESA assessment - What to ask from GP?

Hi, sorry that my first post is begging advice, but I'm not sure I'll be able to get an appointment at Citizen's Advice Bureau before I need to get my appeal form sent in.

Date on my Mandatory Reconsideration Notice is 16 October 2017

I need advice please on what I should be expecting from my GP.  I asked for a letter for the mandatory reconsideration, but my GP looked at me with a blank face, saying he's not keen on these types of letters and wouldn't know what to put in it.  All he did was give me a print copy of his notes for that specific appointment, which did not confirm anything other than that my mental health conditions do exist.

When asking for a letter from my GP, what do I actually ask to be included?  My doctor is either not used to this process or is expecting me to say some magic trigger-word before he'll be willing to help.

Should I also ask for a copy of my medical record?  I've never needed any of this stuff before, but it's quite clear that despite what was acceptable in the past, more is now required.

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Below is a brief summary of my condition and what has happened so far in the lead-up to me needing to apply to the appeal tribunal.
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I have a combination of mental health conditions - O.C.D. (the most debilitating on a daily basis), depression and PTSD.  I had always been declared unfit to work for the past decade. 

My condition is chronic with little chance of improvement (at least for the O.C.D.), but suddenly I get awarded zero points at my work-capability-assessment.  This is the first time my claim has ever been rejected, so I sent a letter in good faith, asking for mandatory reconsideration, detailing errors in original conclusion.  They double-down and more or less told me they think there isn't much wrong with me at all.

I'm under the impression they felt I appeared too "normal" at my face-to-face assessment, and I suspect that they have not referred to my medical records either (which the original form said they had a right to access, which I don't have a problem with).

I have not made a sudden and miraculous recovery, and so if I was unfit to work for the past decade, I think I am still unfit to work.  Naturally, I am taking this matter to the appeal tribunal.

Any advice would be greatly appreciated.

Thanks

P.S.  I have not had any CBT therapy since 2007/2008, and I believe assessors feel this means I must be fine.
I explained that I am not allowed any more CBT on NHS funding because the remaining issues do not respond to therapy, and so I would only get more therapy for new problems, not the existing ones. 
The decision makers have either ignored this or don't believe it's true (I was told this verbally at end of my therapy, I don't know if it's actually written down anywhere).