I‘m tTired.

I woke up early this morning, but I couldn’t sleep again.go back to sleep.

I think you may mean to say that you woke up earlier than usual, perhaps. Like you wanted to go back to sleep like normal but could not. If so, the above correction is a very common expression.

So I’m so tired.

This is a fragment. I have corrected it above, but you could also say this:

I woke up early this morning and couldn’t go back to sleep, so I´m so tired.

I took a Pilates class yesterday, so I‘m really sore today too.

without the "too" it sounds like you are changing the subject, but "too" helps connect this sentence to the previous ideas

But I can feel themy circulation getting better, so I try to take a class three time a week.

"my" is better here because it shows it is about your personal wellbeing rather than just a general statement

I woke up this morning, but I couldn’t sleep againgo back to sleep.

So I’m so tired.

A: "So I'm tired." vs B: "I'm so tired." feels different. A = Therefore I am tired. B = I am exhausted. (it's more like I am soooooooo tired - which isn't proper English written but might be said to someone else spoken). But tired and sleepy are also different. I am sleepy (didn't get enough sleep). I am tired (could be sleep or too much work or exercise).

But I can feel themy circulation getting better, so I try to take a class three times a week.