I have always been lucky and my GP has never doubted the severity of the condition I have, nor the severity of my pain.
I think honesty is the best place to start. You cannot help yourself if you mask the truth or try and keep it together. You need to use the real words that describe how bad it is for you and describe things like the true effect it is having on your daily life, your activities, your mood and your relationships. If you want to cry, don't hold back - he needs to understand how it is affecting you.
It's easy to try and keep it together and you don't want folk to see you falling apart - it's only human to hide the reality from doctors - been there and done that many times. It doesn't help either in the short term or the long term.
Pictures and a pain diary can be valuable tools if your doctor responds to those things. If not you need to try and work out what will make him or her sit up and respond. You might want to think about it and rehearse the conversation or what you want to say before you go (with a friend or partner or just in your own head). Try and anticipate any blocking questions the doctor will ask to try and test whether you are overreacting - perhaps have some actual examples that illustrate what you are trying to say ready beforehand so that you can dispatch those questions by demonstrating just haw terrible the effect of the pain etc is on you.
I spent a lot of time in tears with my GP - he was as keen to explore my mood issues as well as the practical pain and other problems. The tears are sometimes still there but much less so these days. I didn't want to be honest about mood so I was angry and defensive but when I finally fell apart we finally managed to move forward a bit. After that I was less defensive, cried when I felt like crying and was totally honest about how crap everything was. He worked hard to support me - we had a few heated arguments too but he worked hard for me and has never doubted my pain. In fact, he worries that I am am sometimes too inclined to try and tough it out when that isn't helpful for chronic pain management.
Trust is important in the GP patient relationship. My GP trusts me and the accuracy and currency of my knowledge of the condition. If I ask to try something or seek a referral, I take all the info he needs to evaluate it and I explain exactly why I think it might be worth doing. I always give him and his views their place and take on board what he thinks. We agreed recently that I would just 'live with' big flare ups in pain without medicating using fast acting fentanyl products because I already find the fentanyl patches hard work in terms of their fatiguing side effects. We discussed it constructively and because I had read, sought advice from a friend who is a pharmacist and was aware of the risks, it was a conversation of equals, not him telling me what I could and couldn't have. I know that I can always go back and revisit that conversation to look for another outcome if I have new information or if what I am prepared to suffer changes.
So, truth and honesty, examples, tears, taking someone with you who can perhaps back up what you are saying about how badly the pain affects you and no holding back are my suggestions.
You did say that you have tried all the modalities yet you are looking for something more from your doctor. On the face of it that sounds like a bit of a contradiction. Have you really tried everything and the problem is that you are going to have to accept the fact that you will never be pain free? Are you struggling to accept that this is maybe as god as its going to get? Or are there actually still various things you haven't tried for pain management yet and you want to open a discussion about what you can try? Just curious to understand where you are at in the CRPS journey.