this one sounds better for the last sentence.

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if it was me writing it i'd (i would) write it: --
"It is also very tiring because, i'm (I am) sleeping badly and eating unhealthy.  "
Because you need a subject or they don't know who you would be talking about.

^^ 

Today is Monday, but i "do not" (don't) need to work.  It is because I work the night shift.  Therefore, it means I should be working at night in a month.  Working at night is very interesting, because my supervisor doesn't work at night.  It is also very tiring, sleeping bad, and eating unhealthy.

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Benson, hope this helps. i know its hard because we switch our words around in english. while in chinese, its always something important first then the action.
Also, in english you rarely start a sentence with a because and a but.
As for talking about "during" the night, its not in but at. 

Overall, it is very good ^^ keep writing!!!~ if you like i can always proofread for you =].

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