you are not alone! I have had trouble with my chest for about 3 years now. I am 45.
I have a past diagnosis of coronary artery spasm and inappropriate sinus tachycardia.
I too get chest tightness and breathlessness on minimal exertion. Like you, even one flight of stairs makes me out of breath and tight chest. I do try to have a 10 minute walk outdoors every few days, but its difficult. Its is complicated by the fact I have fibromyalgia and feel generally weak and tired anyway.
I am seeing a different cardiologist next week as I have also read about microvascular angina and I wondered if I might have that. It cannot be seen on angiogram apparently as the vessels are too small and from what I have read, can either be the vessels clogged up or going into spasm.
I have been taking Bisoprolol and Nicorandil for the past couple of years which help and can manage ok around the house but trying to walk any kind of distance, even on the flat is a nightmare. I have a GTN spray for when I go for a walk and I think it does help. I do sometimes get chest tightness and breathlessness at rest too.
Tests I have had in the past are:
Chest x-ray- normal
Coronary angiogram - normal
ECGS - abnormal - T wave inversions at rest/tachycardia
Stress test- only managed a couple of minutes but showed subtle changes
anyway, I will see what happens with the cardiologist next week, might be good to get a different opinion