From my writing

Julie, could you please explain the difference in the meaning and using between ( had been done and were done) ( domain and area)?

and another thing please
What’s the difference between (researches and studies)???

Your original statement was “numerous researches had been done in this domain.”
“Research” does not have a plural form. So this phrase should be either “numerous studies” or “much research”.
When you wrote “had been done”, it led the reader to assume that you would follow with some results of the research. Since your next few sentences listed questions about how to take care of one’s health, it was better to say that studies “were done”, insinuating that the following questions were part of the studies.
The use of “domain” was not incorrect, but unnatural. Here is one of the definitions of “area”:
A division of experience, activity, or knowledge; a field: studies in the area of finance; a job in the health-care area.