Remember: this too shall pass! You're more than halfway there.
Practical measures to reduce stress: eat a balanced diet in sufficient quantity and at regular intervals, even if you're busy. Get enough sleep. Get some exercise (hiking, biking, running, aerobics, volleyball - something to work up a sweat): endorphins are our friends. Focus more on your patients and on the material and skills you are learning than on your feelings during clinicals. Consider that dealing with a difficult instructor is giving you experience in dealing with difficult charges, managers, supervisors and colleagues. It's an entire skill set on its own.
As soppy as it may sound, try to find a few positive things that happened during each clinical. It's an exercise in changing the focus.