How can I set boundaries and earn more respect at my workplace?

I am an international PhD student and I am very overwhelmed with work and stress. So much so that when I need to set boundaries and protect and justify my work I am not able to do it. people treat me like a very useless business. I know I should do better at communication but it would be very helpful if you guys could suggest me something how not to be scared and protect my respect, work and time.
How can I set boundaries and earn more respect at my workplace?
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