I don't see any issues with how you used "struggle" in any of these sentences. If I may, I would like to suggest a slightly different way of wording one of the sentences. You wrote "For those who do an intellectual job, that is the daily struggle for those suffering from insomnia." The wording seems slightly off to me. I think a more clear way of expressing this would be "For people who do an intellectual job, those who suffer from insomnia struggle daily". As a disclaimer, I don't claim to be a teacher or an expert at all thing English so certainly don't take my suggestion as gospel truth or anything. :) EDIT: I also noticed something else that doesn't look right. "Small businesses still struggle to be competitive at the beginning in comparison with the bigger one." I'd replace "the bigger one" with "bigger ones". I'm on the fence if "in comparison with" should be changed to "when compared to". The latter sounds a little bit better to me but I'm not convinced that the former is necessarily wrong.