I understand you might have taken up the job with lot faith in your boss, his way of thinking, and later realised the situation you have gotten into which would be overwhelming.
Think about the consequences happens if you take a decision about it, for example what would happen if you continue this way, what if you communicate your boss about your problems or what if you change the job, (writing them on paper helps sometimes) take the decision accordingly.
If you think you can't do it alone. Take professional help with a counselor.
Health Tips
you can get into some activities other than work related to reduce the stress.