Have you considered the possibility that it might be your heart? I developed microvascular endothelial dysfunction after my first Covid shot, which got much worse after my fourth round of Covid. Microvascular dysfunction causes the microvessels in your heart to constrict, especially with exertion (like climbing stairs), resulting in heart attack symptoms: shortness of breath, chest pressure, chest pain, fatigue . . . .
Not every cardiologist is familiar with microvascular dysfunction, but Mayo has some of the best. That's where I got my diagnosis and where I've gotten my best treatment.