The final exams are this week is th/ I have final exams. this week

Final exams (plural, multiple) and week is the "when" of this sentence. Try not to make them both subjects; here week acts as a "what" so you are saying "this is that" instead of "this is during (time)"

Therefore, I spent most of time studying for them today.

The winter vacation will start on this Thursday, and I'm so excited about it!,

Bbecause it means that I will have more time to learn English.

Not preferred to start a sentence with because when you can link them

Also, I like your passion! :D

Speaking of it, my roommate was so mad about the education system. / school system

For a more casual tone, use school system

Howeveryet / but , we still need to spend more time to review and study them.

As a result, we don't have enough time to do whatever we're interested in.

dDiary 1/2

This week is there are final exams this week.

Therefore, I spent most of time studying for them today.

The wWinter vacation will start on this Thursday, and I'm so excited about it!

SCome to speak of it, my roommate was so mad about the education system.

She was confused about why we spend a lot of time attending the lectures.

However, we still need to spend even more time to reviewing and studying them.

As a result, we don't have enough time to do whatever we're interested in.

I feel it only when the exam is coming up, just like now.

But the feeling is stronger than before,. I think the reason isfor this is that I'm goal-oriented now.

dDiary 1/2

This week is the final exams week.

or

I have final exams this week.

Therefore, I spent most of my time studying for them today.

The wWinter vacation will start on this Thursday, and I'm so excited about it!

BIt's because it means that I will have more time to learn English.

This was a sentence fragment so I corrected it to make it a complete sentence.

Speaking of ithat, my roommate was so mad about the educational system.

She was confused as to why we spend a lot of time attending the lectures.

However, wWe still need to spend moreadditional time to review and study them, however.

We avoid using "however" at the beginning of sentences when writing.

As a result, we don't have enough time to do whatever else we're interested.

I feel it only when the exam isexams are coming, just like now.

But tThe feeling is stronger than before, though. I think the reason is that I'm goal-oriented now.

This week is the final exams.

It makes more sense to say: ‘I have final exams this week.’

Therefore, I spent most of time studying for them today.

The winter vacation will start on this Thursday, and I'm so excited aboutfor it!

Speaking of it, my roommate was so mad about the education system.

However, we still need to spend more time to review and study them.

As a result, we don't have enough time to do whatever we're interested in.

But the feeling is stronger than before,. I think the reason is that I'm goal-oriented now.

Therefore, I spent most of my time studying for them today.

or: I spent most of today studying for them.

BI’m excited because it means that I will have more time to learn English.

Alternatively, you could join this to the previous sentence:
“The winter vacation will start this Thursday, and I'm so excited about it because it means that I will have more time to learn English.“

Speaking of itschool, my roommate [was so | was very] mad about the educational system.

“It” doesn’t work in this context because it’s hard for the reader to understand what “it” refers to.

She was confused whyfrustrated that, although we spend a lot of time attending the lectures, we still need to spend more time to review and study them.

As a result, we don't have enough time to do whatever we're interested. in | to do what really interests us.

I feel ithis only when thean exam is coming, (just) like now.

I would omit “just,” but it’s not wrong.

But the feeling is stronger than before, and I think the reason is I'm goal-oriented now.

In English, joining two sentences with a comma is usually considered an error, called a “comma splice.”
https://study.com/academy/lesson/comma-splices-examples-corrections-quiz.html