"What happens exactly is that when I get onto the main road I am filled with panic and start violently shaking"
Well, if that can help, I am prettysure the other drivers are grateful you don't drive.
Seriously, I think you just lack practice and the problem the longer you stay without driving, the more difficult it will become to overcome. (may-be try a therapy ?)
Yeah I am going to be going to therapy but also I moved to a rural area that would be much better for me to learn. I know it isn't safe for me to be on the road in that state. haha