CORRECTED SENTENCES:

I am melancholic.
I feel gloomy for no reason, but not always. = I feel gloomy for no reason at times.

I feel depressed one month every three months. = I feel depressed for a month every quarter of the year.
in detail, for 2 months I live very hard and strive to achieve my goal. = In detail, for 2 months I live very hard and strive to achieve my goal.

but all of a sudden depression comes to me. = But all of a sudden depression comes to me.
After that I start to think like that - why do I strive... why do I have to meet someone... it doesn't have any reason.  = After that I start to wonder why I strive or meet people for no reason. 

just It happens. = It just happens.
in the past, I could not handle this status so I lost my mind longer than 1 month. = In the past, I could not handle this status so I lost my mind longer than a month.
but nowadays I ignore this status.  = But nowadays I ignore this status. 

just I leave my emotion like it doesn't exist. = I just ignore my emotion like it doesn't exist.
And then I can escape from this hell more quickly = And then I can escape from this hell more quickly.