What Causes Itching On The Chest?

It starts with an itch just to the left of the very top of my head. Next is a raking cough from the base of my throat where the notch in the bone is. Then there is a hand sized area at the top of my chest which itches so badly I want to claw at it not just scratch. The coughing is bad enough to pull muscles.

My friends are so aware that they notice as soon as I start to scratch my head. This has been happening on and off for 2 or three years.

I have a hypothyroid problem which is not fully controlled.

Any ideas what on earth this is all about.