I finished the Harry Potter series, and I cried. I finished the Harry Potter series, and I cried.

I finished the Harry Potter series and I cried. I finished the Harry Potter series and cried.

The second "I" is not incorrect but unnecessary because it's clear "I" is the subject

I finished the Harry Potter series and I cried. I finished the Harry Potter series and cried.

By the way, today I ate delicious noodle vermicelli today! By the way, today I ate delicious noodle vermicelli!

I ordered vinegar, but I forgot to add it in! I ordered vinegar, but I forgot to add it in!

I ordered vinegar but I forgot to add it in! I ordered vinegar but I forgot to add it!

-'in' is not necessarily wrong, but it isn't necessary and it sounds better without it.

I ordered vinegar but I forgot to add it in! I ordered vinegar but forgot to add it in!

Same note as before

I ordered some vinegar but I forgot to addput it in!. I ordered some vinegar but I forgot to put it in.

I'm not sure exactly how to phrase it; the phrase "put it in" isn't very natural.

I’m so hungry writingjust thinking about it now!!! I’m so hungry just thinking about it now!!!

I’m so hungry while writing iright now!!! I’m so hungry while writing right now!!!

There are a couple of ways to say this. To just talk about the time, you can say 'I'm so hungry right now.' You can also just say "I'm so hungry now.' A connection is needed between hungry and writing. So you can say 'I'm writing right now and I'm so hungry.' Or. 'While writing this, I'm so hungry.' Or, "I'm so hungry while writing this."

I’m so hungry writing ithis now!!! I’m so hungry writing this now!!!

I’m so hungry writing it nownow as I write this!!! I’m so hungry now as I write this!!!