Current School Life

Recently, I have (Nowadays, I) had many assignments to write, some of 3,500 to 4,500 words. (whose words requirements are 3500 and 4500 and so on. ) This would be a challenge for me in Japanese, never mind English. (I have been upset because even if they are in Japanese it's difficult and hard work for me, I had to write so many words in English.) 

(But) Yesterday, at last, I completed them all and now just need (, eventually, I've been done every assignment!
Remaining what I have to do is) to study for only one exam.
It's not easy because I need to achieve (the volume of it is) 60% in the exam or will fail. (. That means if I can't get some marks I'll fail. )
I still have something further to study but I'm not so motivated now.
Usually, once I complete something, I tend to lose focus (motivation)...That's my problem..haha

Haha..... I have simplified it a little.

I changed a lot of your sentence structures to make your journal entry sound more natural. Hope it helps!

My current school life

I've recently had many assignments with word requirements of 3500 words, 4500 words, and so on.
This has made me feel very upset, as such composition lengths in Japanese would be challenging for me, let alone having to write in English!

But yesterday, I eventually finished every assignment!
The only thing I have left to do is study for one exam.
It won't be easy because this exam is worth 60% of my grade, meaning I will fail should I not score high enough.
I still have some things to study but I'm not motivated now.
I always lose my motivation once I complete something... That's my problem... haha

Current school life

Nowadays, I had have many assignments whose words requirements are 3500 and 4500 and so on.
I have been upset because even if they are in Japanese, it's difficult and hard work for me. I had to write so many words in English (><)

But yesterday, eventually, I've been done I finished every assignment!
Remaining What I have left to do is to study for only one more exam.
It's not easy because the volume weighting of it is 60%. That means if I can't get some marks, I'll fail.
I still have some things to study but I'm not motivated now.
Usually, once I complete something, I lose motivation... That's my problem... haha