The way we learn is different for everyone, but one thing remains the same, the day we stop learning is the day they nail the lid shut !!!!
At this point I would normally suggest a change of instructor but you've done that. However, have you changed instructor group as well? By that I mean are you still flying with guys that are in their 20's and are building hours for that first airline job (no disrespect there by the way, some outstanding instructors in that group) or have you tried flying with the old flying instructor, in their 50's or 60's even, maybe retired from the airlines, been teaching for 20 or 30 odd years. At your age there can be a resistance, if not at the surface, it will be there, to take instruction from a "young kid" In normal life this doesn't happen, in nearly all walks of life the person doing the training will be older than you. In the flying world this is just not the case, but hours are the ageing factor, not years. Once you accept that it might get a little easier. Try asking the CFI to take you up for an hour as a progress check.
Otherwise, I think that you are being hard on yourself, and that in itself will create a stress in the cockpit that will not make things easier for you. You've now been in the circuit for a good while, and it can be a boring place to be, and you are wondering why you are doing this? So next time ask your instructor to skip over the circuits and go for a spot of nav. Pick a field that you fancy going to and get them to teach you how to get there and back. First it will be a break from the same old circuit, it will re energise your interest (it did for me) as you can see what the benefit will be at the end of it, and chances are when you get back you'll make the perfect landing as you'll have had a nice day out, done something different and will be nice and relaxed. I am sure others here will agree with this, and if not try it anyway, what have you got to loose?
As for being 50 hours in with no solo, this is a marathon, not a sprint. Everyone gets some hang up at some stage, and one day it will all suddenly fall into place. Keep in mind that the older you are the longer it can take to master a skill. Again this is not a dig at old people, it is a matter of fact. In driving circles it is reconed that you need 1 hours tuition for every year you have. Accept this and you will be able to move on without beating yourself up anymore.
Finally if all this sounds like rubbish, ask yourself one question, why am I learning to fly? One of lifes great acheivements? Something to do? Crap, like all of us you do because you enjoy it. If you never go solo does it really matter? For that one hour a week (or whatever) you are free to travel at high speed legally and experience something that only a small handfull of the population will ever experience. The freedom of the skies, so enjoy it for what it is. I am reminded of a tale from a few years ago at a flying club in the north of england. 2 old guys used to pitch up on a Saturday morning once in a while for a spot of flying. Both in the "autumn" of their years and had one time flown military aircraft of the propellor variety in anger. One of these WW2 guys was blind, the other deaf. Obviously they couldn't hold medicals so they used to go off with an instructor, who swore that the blind pilot could fly better than a lot of sighted people, they were never going to get licences, but they enjoyed the thrill of being in the air so that's what they did.
Whatever you do, enjoy it!