I`m back home!

After a one-week long business trip, I finally came back home today. Shanghai is really cold. I felt it on the train as near as I was approaching to the terminal. [Or, "Shanghai is really cold as I felt it on the train as the terminal neared"]

But Upon reaching/arriving when I arrived at home, it's so warm and cozy once more comfortable again! [Not wrong, but this is better]

The only thing too bad unpleasant thing is that tomorrow is Monday.  This meant that my weekend was gone I have to continue to work after a non-rest weekend!  Again what you wrote is not wrong but too wordy.

I`m back home!

After a one-week long business trip, I finally came back home today.
Shanghai is really cold, I felt it on the train as near as I was approaching to the terminal.
But when I arrived at home, it was so warm and comfortable again!

The only bad thing/It's a shame that too bad is that tomorrow is Monday, as I have to continue go back to work after a non-rest weekend without resting!