dispressed and disappointed for my work

Actually, everything has its bright side, when you feel the stress, you can also take it as an opportunity,  the stress comes from the expectation that you need to obtain sufficient English proficiency to perform your work. the opportunity is you've got many chance to practice your English. you are paid for speaking in English.
see, many people are paying foreigners for the practicing.
meanwhile, when you get used to it, English will become one of your competent, "No pains, no gains", just keep it up, Every cloud has a silver line.
I am not a native English speaker, I can not even count how many sleepless night I have been spent on learning English, it is not because of any favorism to westerner, it is just because language is a kind of skill, like computer, biological and etc. and providing you pay faithful effort on that, you will definitely make it..