Today I only slept (for) 5 hours, so I was sovery tired at school during the whole day and I struggled to focus. Today I only slept (for) 5 hours, so I was very tired at school during the whole day and I struggled to focus.

"so I was so" - repeating so sounds a little awkward.

Today, I only slept for 5 hours, so. Because of that, I was so tired at school during the whole day and I struggled to focus. Today, I only slept for 5 hours. Because of that, I was so tired at school during the whole day and I struggled to focus.

Today, I only slept 5 hours, so I was so tired at school during the whole day and I struggled to focus. Today, I only slept 5 hours, so I was tired at school during the whole day and I struggled to focus.

I had classes of physics, philosophiey and eEnglish class which is the one I prefer above allmy favourite class. I had classes of physics, philosophy and English class which is my favourite class.

Names of languages and nations are usually capitalised. Replaced "prefer above all" with more natural phrasing

I had classes ofin physics, philosophiey and eEnglish class whic. English is the one I prefer abovemost of all. I had classes in physics, philosophy and English. English is the one I prefer most of all.

I had classes ofin physics, philosophiey and eEnglish class which is the one I prefer above alllike the most. I had classes in physics, philosophy and English which is the one I like the most.

When I came back home I played pubg duringfor an hour but still di(haven't / hadn't) started my biology homeworks yet When I came back home I played pubg for an hour but still (haven't / hadn't) started my biology homework yet

"I played during an hour" - At some point in the hour, you played pubg (unnatural - you could have played just one minute) "I played for an hour" - You spent 60 minutes playing pubg "hadn't started my biology homework" - you played pubg before doing your biology homework (but maybe you've done it since) "haven't started my biology homework" - at the time of writing, you still need to start your biology homework

When I came back home, I played pubg during an hour butPUBG for an hour, even though I still didhaven't started doing my biology homeworks yet. When I came back home, I played PUBG for an hour, even though I still haven't started doing my biology homework.

PUBG is preferably written in all-caps, so let's do that, too.

When I came back home, I played pubg during an hour but stillfor an hour and didn't started my biology homeworks yet. When I came back home, I played for an hour and didn't started my biology homework.

I hate biology (and the teacher as well). I hate biology (and the teacher as well).