LThe last two weeks when I was working early shift, mid shift.

Colloquially this is okay, but it isn't really a complete sentence. Better if you combine it with the next sentence, something like: "The last two weeks when I was working early and mid shift, I decided I would do as much exercise in my own time as I could."

I decided that in my own time I will doingould do as much exercise as much as I could.

"will doing" is very bad. "will be doing" is the correct form for that tense, future progressive. But using that tense here is a bit unnatural. This future-in-the-past construction is better, because the decision is in the past, but the action was in the future *when you made the decision*.

So, I did, and I was happy about that.

Even that isn’t much works to do for the night shift.

It's really difficult to understand what you're trying to say here. Maybe "Even though there isn't much work to do in the night shift, I will feel tired the next day"?

I will feel tried inired the next day.

I can't explain why, but "in" feels very strange here. It does seem like it should fit, but it doesn't. Prepositions are so difficult.

So, my plan for the week willis just to stay home and rest.

Or "my plan is that I will just stay home and rest".

This is the second day of the week.

It doesn't feel obvious enough to omit this.

The fact that mMy body did feels tired because I stayed up all night.

Many problems with this sentence.

But staying home and taking rest is boring.

"resting" is more natural here, but this is okay.

I need to think of something to do rather than just doing nothing.