Also you might be interested in joining "Mental Health Support ".

The breathing issues themselves can be causing what you are feeling.
I have friends with breathing issues and this is common. Please revisit your Doctor! I know it's hard - but it's really the most likely contributing factor. (At least phone to see if the test results showed anything).

After that consider therapy and medication. I know that would be difficult too - but it might well be worth it to get your enjoyment of going out back.

Perhaps you need to speak to a counselor or therapist. Agoraphobia can happen with anxiety or trauma, and grief can cause that as well. As someone who's struggled with this at one time, I can tell you it's possible to manage and overcome it.

Go back to the doctor and get that diagnosis.

I know exactly what you're talking about, and suffer from this myself.

Anti anxiety medication and exposure therapy as well as other therapy. This is debilitating and only gets worse.