I have stress / I feel stressed / I'm stressed

[Mnemon]

a. I have stress.
b. I feel stressed.
c. I'm stressed.

Do they all sound natural to you?

 

[Rover_KE]

a. doesn't.

 

[emsr2d2]

For me, c is most natural, b is OK, and a is grammatically correct but I can't imagine anyone using it.

Note for future - in your title, there should be no spaces either side of a slash. It should have looked like this:
I have stress/I feel stressed/I'm stressed