A lot of good advice here from some and some that I would also have to say is probably not all that helpful. As a somewhat experienced instructor I would have to agree with Luke and Seventhheaven. I have not come across many students that I would say are incapable of making the grade. It seems especially true in this case as some of the issues you are currently having seem to be things you did in the past without much difficulty (eg airfield rejoin etc).
This makes me think that it is just a mental block and with that viewpoint I feel the best advice has already been given, take some time away from aviation. Get away from it for a while and come back with some renewed passion and vigour!