I would definitely see your doctor again. First, rule out anything that would be heart or lung related. That is through some testing. But then if it does turn out to be stress again, what can you do? Are you anxious? Going through a tough time? I have similar symptoms and was told it is anxiety and stress over a family situation. It's hard. I'm trying to get some exercise, sleep enough hours, eat well and take calming breaths, do meditation.
In the meantime, these articles may be of benefit:
2005: https://www.aafp.org/afp/2005/0415/p1529.html
2012: https://www.aafp.org/afp/2012/0715/p173.html
2020: https://www.aafp.org/afp/2020/0501/p542.html
You should see your doctor again for further workup and management.