My Diary

Today the weather is so nice but the temperature is colder* than recently. Last Thursday it rained and I fell backwards and landed on my buttocks. My home is located on the middle of a hill. Unfortunately the hill is very steep so I have bruises on my arm and buttocks. It is very difficult to keep one's balance on a slippery steep hill. I will be more careful from now on.

*is more cold than, or, is colder than. Never 'is more colder than'. Similarly 'is more hot than, or, is hotter than..' etc

**all in the present tense, since 'nowadays' = now (present).

Very well written!

my diary

Today the weather is was so nice, but the temperature is more colder than these days. Last rainy thursday Thursday was rainy, and I fell backwards and landed on my buttocks backside/butt/rump. My home is located on the middle of up a hill. Unfortunately the hill is very steep. So I have bruises on my arm and buttocks backside/butt/rump. It is very difficult to keep the my balance in on a slippery steep hill. I will be more careful from now on.
Nowadays, I was I've been so busy. Therefore sometimes I have make some mistakes that I didn't expect. When I make the same mistakes were repeated over and over, I want to escape from the situation I'm in. So I planned the a trip for in order to relax. Next month I am going to another country. I look forward to the trip.

Good job! I can understand what you are saying, just some changes to make it more natural.

One note: remember to capitalize "I".  "i fell backwards" should be "I fell backwards"