Complex health issues are really difficult and always bigger than the sum of their parts. In my personal experience anyway...
Talking with your therapist about it sounds like a good idea. If you've had it a long time (how long have you had it btw?), then there's gonna be a lot of grief feelings that wanna come out. If you can, let them come out. And if your body wants to shake, let it. It's the body's way of releasing trauma.
Have you told anyone in your family? Or a friend you trust?
From what you've written, I wonder if you may have a condition called anismus. With shy bowel, if the sufferer is in a 'safe' toilet with no time pressure, they can poop ok generally and feel like they've emptied their bowels - had a good crap basically. Their body may take time to feel ready to go, but eventually they'll get the urge. (The only exception is if there are no toilets that feel safe.) Have a look at the wiki page for anismus and see what you think.
That's enough for now. Hang in there. Keep posting. It helps other people too as well as you.
One practical thing: don't go to the toilet twice every hour to 'try'. It won't work. Have a read of my book: it explains why in there.
In the meantime, if you get the compulsion to go and 'try', say to yourself, "a watched pot never boils". Go and do something else, try doing a task that involves using your hands like doing the dishes, mending a piece of clothing, cleaning, etc. Or other tasks like fixing a computer issue or some other problem, DIY, anything that absorbs your attention. The more absorbed you get the better. If - and in your case it's a big if - you get an urge to crap, wait til it gets stronger and you really need to go to the bathroom.